In any other field people would be praising Lucas for not wanting his artistic vision compromised. Imagine if someone wrote a new Harry Potter book that Rowling didn't like, the fans would be scathing towards the new creators, not to her. But fans have decided Star Wars is their thing, and the vision for it that Lucas had is not something they want. Instead what people want is familiarity, safety, and focus groups, instead of technical innovation, experiments and different approaches to storytelling.
Lucas wanted his films to be distinguished from everything else in cinema, Disney wants their films to be indistinguishable from every other Star Wars. Lucas drew on hundreds of crazy influences, from poetry to mythology to war films to B-movies... Disney's Star Wars draws almost exclusively from Star Wars, and nothing else.
And that's what happens when you go from one man's artistic vision to a corporate focus group approach to storytelling. The fans may enjoy it more, you may sell more tickets, but in the same way the people who write modern James Bond novels will never be Ian Fleming, even if they're better writers, Disney's Star Wars may be beloved and make lots of money, but it sits in an entirely different artistic box from the six Star Wars films Lucas made, which is why he absolutely has the right to comment on the direction they've taken his work.