(*Before anyone starts complaining that magic doesn't exist in the Transformers universe, I will point out that the Transformers exist in the same Marvel universe as Spiderman, Doctor Strange and the Scarlet Witch.)
Actually, it was a wee bit more complicated than that, something that the
TF Wiki page on the Marvel comics explains.
Back in the 1980s and 1990s, the standard arrangement for comic books in the US and Canada was was that they were each printed monthly. Each monthly issue had 25 - 30 pages of story, and most comic books had their story backed up by advertisements (both in-house and paid external ads), a 1 - 3 page letters section, one-page comics, 1 - 2 pages of editorial material, and/or 1 - 3 pages of character profiles. Marvel US kept to this standard schedule when publishing Transformers.
Marvel
UK, however, was printing things
weekly or "fortnightly" instead of monthly. Each weekly printing consisted of about 11 pages of story, coupled with a back-up story (which were often stories from another franchise entirely), one-page comics, a letters section, advertisements, and editorial fare.
The folks at Marvel UK realized that because of the difference in printing schedules, it would be impossible to simply repackage the US stories for sale in the UK: each monthly US offering could only be broken down to make three weeks' worth of books for UK sales, and so some sort of "filler" was needed to cover that fourth week. As a result, the Marvel UK honchos assigned a few individuals to write various stories for the series; the comics would go back and forth between the US material and the UK material for the duration of the run.
It's true that Spider-Man, Nick Fury, and Dum-Dum had cameos in issue #3 US, and issues 5 - 7 US involved The Savage Land; this was done to boost interest in the title, which was on shaky ground when it first launched due to issues with the US government.* However, Marvel US
quickly moved to retroactively declare Transformers separate from the main Marvel universe; by issue #10 US, there was a general prohibition on anything relating to Marvel heroes appearing in the Transformers title. The only exception was the character
Circuit Breaker, who was originally created for the series but was shoe-horned into the "Secret Wars" event so that Marvel could claim ownership. In fact, to my knowledge, the only Transformers crossover series during the remainder of Marvel's possession of the Transformers license came with G. I. Joe.**
However, Marvel UK had no such qualms about having their franchises cross over. This led to a greater degree of interaction between the Transformers title and the other Marvel UK titles, including
a key story arc in which
Death's Head featured prominently.
Either way, Marvel no longer has the license. The North American license for the franchise went to Dreamwave Productions circa 2002 (with Devil's Due, another alumnus of Image Comics and the then-license holder for G. I. Joe, producing a Joe / TF crossover), and when they went under*** the license was given to IDW. IDW worked out an agreement with Marvel to produce a brief Marvel / Avengers crossover, but that series is essentially self-contained and so does not impact the hero-free IDW main Transformers universe.****
*Due to backlash over a Hot Wheels cartoon done back during the 1960s or 1970s, the US government forbade the practice of having toy lines tie into children's television series. However, a loophole existed in the law that allowed for Marvel and DC to have children's shows based on their comic book characters
and have licensed toys in stores at the same time. Hasbro spotted this loophole, and so in 1982 they decided to test the waters by working with Marvel to produce a comic book series that would tie in with the revived G. I. Joe line... with Sunbow studios (owned in large part by Marvel) producing animated advertisements to sell both the comics and the toys. The next year saw a five-part animated mini-series (which in some markets was broadcast as a single made-for-TV movie), which Hasbro got away with since the comic series had already been around for several months by that point.
But with Transformers, things were a wee bit shakier. Hasbro was going to launch the toy line, comic book, and television series within months of each other, creating a risky situation for both Sunbow and Marvel since no one knew if the franchise would succeed. The comic book was originally billed as a four-part mini-series, with two different endings being written in case the toy line flopped. The cartoon, meanwhile, started out with a three-part mini-series that had an open ending. Marvel decided to have Spidey appear to draw attention to the franchise, but it turns out that they needn't have worried; the franchise was an instant hit, and by the end of the year the government was forced to quietly abandon their prohibition.
**Two G. I. Joe / Transformers cross-overs took place during the Marvel US period. The circa 1987 cross-over was largely self-contained, and aside from the character Bumblebee being rebuilt into Goldbug and the character Dirge being killed the series had no effect on either title. In fact, the cross-over event would not be recognized in either title until 1993, when a second cross-over had one of the Autobots "remember" working with the Joe team before (despite said character having not been involved in the 1987 crossover).
Thing is, Marvel UK originally decided against reprinting the US crossover in favor of producing their own Action Force / Transformers crossover. This created something of a continuity problem as it required Marvel UK to explain how Bumblebee became Goldbug, and so the character was added to the "Fallen Angel" story arc at the last minute.
***This may be something of an oversimplification, but here goes. Dreamwave was owned and operated by brothers Pat & Roger Lee, with Pat also serving as an artist on various comics and other projects. The Lee brothers saw Dreamwave as their own personal bank account, and so used company funds to subsidize their high-rolling lifestyles. This backfired spectacularly when the company lost an incredible sum of money on a poorly-advised business deal. The money that the Lee brothers siphoned off would have been a more than adequate bulwark against the losses, but without it the company was now in dire financial straits. Rather than own up to their sins and re-invest their own personal assets into the company, the pair instead came up with a series of excuses to avoid paying their workers while still publicly telling everyone that the company was fine overall. It wasn't until after some of their Transformers team publicly quit over the matter that anyone came to realize how bad things were, but by then the Lees had already funneled most of the company's assets into a new venture; they declared the company bankrupt shortly thereafter, and to this day a number of Dreamwave employees
still have not been paid in full for services rendered.
****About a year or so back IDW
did launch a series entitled "Regeneration", which does follow on from where Marvel's original 1984 - 1991 series left off. However, that's separate from what they've got going now.
