Spoiler warning, kind of, if you haven't watched.
With Steven universe ending I feel.... Like it ended the way it deserved. It ended with Steven growing up. Not him being grown up. He spent most of the show pretending to BE grown up. But he's not. He wasn't. That why what happened... Happened.
He quite literally was a child playing the part of a leader to people thousands upon thousands of years older than him. He may have gotten guidance from everyone, in some way or another, but he never really had parents. As much as I know its common to think the gems raised him, or Greg raised him, they didn't. They gave him necessities, they fixed the parts that exploded and flooded out, but they never actually were... Parents. I'm not sure quite how to explain that, but it's how I felt about it. Steven will never have the chance to be an actual child. He got that taken because, no matter what, he wasn't a gem, and he wasn't a human. Or at least got viewed as such, so he wasn't treated quite like either. It meant he either got left behind, made to lead, or was with loved ones, chilling, but he was never really raised by anyone, in the sense that someone helped guide him, and, as evident by the monster Steven, let him have a safe place to vent. They may have let him, but after so many scenarios where he had to take care of everyone else, he didn't feel he could. Because, well, how's that fair? (In the eyes of the person helping others) because Steven knew, to an extent, what everyone else was going through, he didn't want to burden them.
It's fitting that he gets to be by himself when he leaves. It makes so much sense. But I feel that's also why it's such a heavy ending. He finally gets to be independent, and that includes no long having anyone else reliant on him. It's almost a regression, but he can't regress to childhood, and stop the damage. Hes already damaged, and it's giving him a chance to rebuild himself, and, in the scenario that a part of him won't fit because, well, he's part flesh, and he grows, he's not pure gem, so it obviously won't fit back perfectly, or even at all, he may need to toss a few pieces out. And he can fix those parts.
I feel that appeals to so many people, and makes them feel like they just want to be kids again, but they can't. Because we grow, and we can't fit back into the place we came from. We can't fit back every piece of ourselves. And it's like this part of your life that been there for so long, that it hits a nerve now that it's ending. You can't go back, but you want the good parts again. And, no, that doesn't apply to everyone, but for so many people, it does. And I hope everyone works out what they need to.