Uhh, I tried to stay out of this discussion, but I see strong parallels to the old vs new forum debate in the Blender UI debate here.
I think it is a really bad idea for communities and volunteer driven open source projects to cater only to existing users.
Even if you don't aim to grow your user-base, it is of vital importance to to have a certain size as only a small percentage will actively contribute to maintenance and development and natural churn of users means that any such projects are in constant need to attract new users.
This is somewhat counter intuitive for what appears to be nonprofit endeavors driven by existing users, but to anyone that has been running a (surviving) community for a longer time this should be self evident.
But the constant complaints from the vocal minority of conservative long time users that fail to understand this dynamic is really getting on my nerves.
And anyways, there is nothing really objectively better or worse on the old vs new Blender UI, but yes it did follow industry fashion. Following such fashions is a way to effectively signal to new users that the software is under active development with a heathly developer community that is open to new ideas. Sticking with the old UI, while pleasing existing users, signals the exact opposite and thus becomes a self-reinforcing loop that ultimately kills a project due to a lack of contributors and maintainers.