Why is this idea so popular? (rant - movie spoilers)

So we know that by the end of Movie 3 Eggman has basically performed his third (?) fakeout death. It's true that this one feels pretty definitive, considering his final selfless act to save the Earth and his final speech to Stone. But now with the recent news from Jim Carrey being willing to return to new movies people are now speculating on his role.

And I have to ask, why is the idea of Eggman Nega so popular? Personally, I think that would be the worst way to keep him in the movies. Eggman Nega has barely any relevance in the franchise outside of the Rush games, and if anything, he is basically Blaze's nemesis, not Sonic's. Having a carbon copy of the doctor who has no personal vendetta against the heroes just feels... dull. Plus, why are people justifying it like he could be Robotnik's descendant? He has already stated even within the movie that he has no family, no wife, no kids. "The Robotnik name dies with me". So how can Eggman Nega be a descendant then... I can buy a different timeline/dimension/planet, but not descendant. It doesn't make sense and it's not plausible narratively speaking, the movies would need to justify way too many things for it to be compelling.

The most realistic approach here is that Eggman survived, simple as that. If you don't think that's possible, let me remind you Shadow has Chaos Control, and Shadow survived. It's not farfetched to assume Shadow saved him at the last second as thanks for helping him save the Earth. Does it feel cheap and like it invalidates Robotnik's sacrifice? Maybe. Do I care? Not much really... Eggman is Sonic's eternal nemesis, to have one without the other just wouldn't feel the same after a while.

The next best thing, if Eggman is to remain dead, is for him to be a fake created by Metal Sonic/Neo Metal Sonic, which sounds far more plausible than Eggman Nega, seeing the mid credits scene.

I apologize for the rant, but I needed to get this off my chest, because even if we look at these movies as fans, we also need to realize the movies need to build its own universe tactfully and progressively.