Board Thread:Questions and Answers/@comment-6024554-20130502175717/@comment-4651179-20130504200741

There's a theory Marvel saw the Ultimate Universe was being too similar to Earth-616, and they decided they needed a big event with a lot of casualties to change the course in which the Ultimate Universe was going.

So they commited the mistake of turning the Ultimate Universe from a retelling of classic stories (its original purpose) to a completely different universe where mutants were created by the government and were criminals, the X-Men and the Fantastic Four were no more and a lot of heroes died.

And the alienation from its main purpose got worse: They killed off Spider-Man, even if it was in an epic and emotianally powerful way and his replacement was good, it was a terrible mistake, because Ultimate Peter Parker was the only Ultimate thing which never stopped being awesome.