The OG didn’t start as a cohesive Trilogy, either. It was just not made by a bunch of hacks or yes men.
People like Kasdan came back for it.

It's pointless to play the guessing game with what went wrong behind the scenes, since we can't know, there probably was the usual clusterfuck of people trying to jam their opinion in, creatng this Frankenstein's monster of a trilogy.
What we
can see, is what works and what doesn't, though.
The new characters worked as a jumping off point; they weren't just carbon copies of the old ones, they were charming and energetic enough, they could've easily carried the trilogy.
But then they didn't give them a clear arc, and they muddled the water with the constant call backs and obsessing, almost, with the old cast.
But when you start off with a 3rd Death Star, i guess it's a sign of things to come.
I'll add that turning Star Wars, from a universe of space adventures, into the endless saga about the "Skywalker lineage", was always a dumbass move; it killed its potential for creativity.