It's not true. He cared, he said so. He considers them his babies, and mentioned that (and was forced to apologize after) that he felt that he sold them off to the white slavers.
He cares as much about it as the fans if not more, and that's why he's coming back to take care of it, because they did such a horrendous job with it. Even despite mentioning what he did about how you deal with an ex: you don't call, you don't check up on her, you don't pass by her house. But because they so disrespected his legacy in an unexpected way, he's coming back.
What I mean is, he didn't seem to care enough to keep creative control. It's easy to talk afterwards, especially if they didn't turn out in a way people wanted.
And fans often care a lot more than the creators. To an unhealthy degree even. Lucas can't answer questions in interviews about the lore that fans commonly can. Not that there's anything wrong with that, but he didn't strike me as particularly enthusiastic about the world he created.
Him wanting to work on new films is just a rumor though, isn't it? You said it with certainty, so I'm unsure.
Though it wouldn't be surprising if it happened since they seemingly did something similar when they booted Rian Johnsson and had JJ come back.
The prequels were disliked by the fans because they didn't reach the level of quality of the originals. It's a small sin. The sequels were hated because they insulted the originals in many ways, it's on a whole other level it's incomparable.
At a distance, you could chalk up the reception of the sequels as not reaching the height of the originals as well. But people's specific complaints about both the sequels and prequels are of course more nuanced than that. (Though personally I don't think anything comes close to how they messed up Luke in 7-8).