I am going to defend Lucas here. From everything we know, this is in no way his fault.
The issue, at its core, for Lucas was that he is not getting younger and there was no one to 'take the flame' so to speak. No singular head at Lucas Films besides himself and thus Star Wars looked fit to die with him. So, he really only had two options:
1: Find someone to succeed him.
2: Sell to someone who could do it.
None of his kids wanted it, none of his staff were fit to take it, so it really only left 2.
Now, the obvious objection, "Well selling to Disney was a bad idea".
Well, then to whom? And it is not like Lucas just pawned it off willy nilly. He sold it to the person he had worked with before, someone he personally trusted. Bob Igor. Now, Disney gets a lot of hate in here, and not entirely without merit, but Igor is not at fault for Star War becoming a complete trash show, but we'll get to that. For now, all you need to understand is that Lucas had worked with and was friends with Bob Igor.
Now, before leaving Lucas wrote up what he had planned and presented it. Igor said they would take it on advisement, never rejecting or accepting it outright. To then ensure his will, Lucas made the person at the head of it be someone he trusted. Kathleen Kennedy. A woman who he had worked with for quite some time, who had a pedigree, and who was on good terms with Lucas. Someone who he believed would advocate for his ideas.
Now, here is where it comes together. Lucas has, at this time, given the franchise to someone he was given reason to rust, ensured there was someone high up to advocate for the films, and provided what he could to put the new trilogy on the right path. He has, at this point, done literally everything he could.
So, what went wrong? Well, its the same reason I need to preemptively defend Bob Igor. Kathleen Kennedy happened. Lucas had installed someone he thought eh could trust, and Igor saw someone who would make fairly 'standard' Star Wars movies to ensure they made bank on a costly purchase. Instead, Kennedy revealed her stripes as an ideologue and UTTER lunatic. She immediately made it clear she was not going to defend a single thing Lucas wanted, which Suited Igor who didn't want to take any of the Risks Lucas did, but then made every decisions possible that could piss of the fans,m which fucked over Igor.
Put simply, the fault lies not with Lucas, but with the woman who backstabbed everybody.