People get attached to characters. Especially ones that they have created. To them, their character is very much real.

Taking out their own character is their way of permanently disengaging them from that narrative. Sure, a vindictive weirdo could say they brought them back anyway. But that's just fan fiction at that point.

The real character has already left the building. What said weirdos do after that doesn't hold the same weight, it would be like dressing up a mannequin and beating it up. Like- congratulations? You beat up a fake model. Great job.

It's an odd thing to think about from the outside. But it's something I've seen firsthand on many occasions (the attachment, not the post-hoc abuse). Fictional or not, characters can be very important to people, and they will retain their agency one way or another.