My new crackpot theory is that Mobius looked at his timeline.
He looked sometime around the start of season 2. Since the beginning of this season Mobius has been a bit less motivated, he’s kinda goofing off, and he’s always trying to get food or drinks. Not quite the sharp minded analyst he was (I mean really- Brad running should not have been a surprise). Which could easily be explained off as coping from the trauma of learning everything was a lie and they’ve been pruning innocent people for nothing.
We have a Don. Don who is a bit like Mobius but who doesn’t seem as in control. Who offers Loki drinks before knowing him. Who’s not as sharp because he hasn’t needed to be. He’s a single dad who sells jetskis not an analyst who’s been doing his job for a millenia or so. He doesn’t seem very happy either with his jet ski shop or his home life. He seems more stressed than anything.
It’s almost as though Don’s life is bleeding through to Mobius. Mobius said he didn’t care if it was bad but he didn’t want “something good rattling around in there” but what if it already was? What if it was a “good life” but not one he likes, not a life he wants. What if that’s the reason he got so upset with Brad, the reason he shut down with Sylvie. Because he already looked and he still wants to stay at the TVA. They say his life is not real but it feels real to him. Not just until the crisis has passed, but indefinitely. He likes what he does and doesn’t feel like Don but his memories are still there and he feels guilt over “abandoning” the kids by not returning. Kids he has only around 11 years of memories of compared to a thousand or so at the TVA.
On top of that everyone seems to think that the best thing to do is to go back to their timelines- they all want to back to where they came from. So Mobius feels worse and just claims he hasn’t looked at his. It’s why he got so aggravated with Loki too, because he wants to stay with Loki and he doesn’t want to go back, but Loki is trying to help and doesn’t realize that Mobius has already decided. And of course when Loki sees Don and his life he decides that Möbius is not coming back. The classic “If you idiots would just talk to one another” trope.