>>281973087
Easy, Ichigo is forced to stay in Soul Society because end of series he's too strong to continue staying in the Living World without breaking the fragile seperation of worlds making Yhwach the winner despite his defeat.

It's not even a stretch either when you remember that fucking VC are limited to 20% of their strength which includes people like fucking Momo and Omaeda.
Ichigo isn't going to restrain himself if something is going down and he sees it. Remember at the start of the series where he's giving Rukia attitude about doing her job while he has her powers and she drags him to a park where a Hollow shows up?
Ichigo tells Rukia that he doesn't give a shit but if something happens where he can see it, he will do something about it.

Kubo set this up with Soul Tickets like that other anon mentioned which would let his friends and family visit him.

I genuinely believe Kubo went with Ichihime as a final fuck you to his audience, how else would you explain the second half of TYBW?