The problem is simple:
They used the open-source style goodwill generated by the old thing called GNOME, as it existed with Linux, to bootstrap their current popularity, and this is to me, dishonest.
They used a different style and direction. Had they changed the name and/or been clear and upfront about the fact that "this new my-way-or-the-highway thing isn't the Gnome you're used to," then I could defend them.
Call it something new and let MATE have the old name.
But they're not interested in doing or even acknowledging that. Let the mud slinging continue.