So they killed Peter Parker so they could replace Spiderman with a ...
... Kind off. It was a Spierman in a parallel world to ours. So they did not kill the Peter Parker you know.
Our world was not part of this story.
Well, it was kind of the straw that broke the camel's back for the Ultimate Universe when they did that. They killed off a ton of popular characters already in a terrible crossover event called Ultimatum a few years before that. Then they killed off the Peter Parker/Spider-Man of that Universe just to replace him with a minority. Just for the TC whenever you have the time, watch this review of Ultimatum.
Also they have used aspects of the Ultimate Universe even in the first Raimi Spider-Man movie. Like Harry and Mary Jane going to highschool with him and him getting bitten by the Spider while on a field trip in school. In the original Spider-Man comic he was bitten by the spider at an event he went to by himself after school. Also in the original comics, he didn't meet Harry, Mary Jane, or Gwen Stacy til he was in college.
they did it because they are dumb sjwsshare