My immediate answer - Sonic fans.
I don’t really know what Sega and the Sonic Team can do anymore to make these fans happy. They’ve revisited the classic formula a few times, they tried going modern routes, they tried 2-D sprites in some entries, they try going full 3D and whatever. Nothing ever seems to be enough and that’s even when they’ve tried listening to the fanbase a few times.
Nothing seems to matter, regardless. The fans will find something to be upset about with Sonic. Anything.
Not to detract but Sonic mania. It did everything right. Everyone loved it. And then they just kicked out the creative team behind it and decided to never make a sequel since it showed how poorly sega had been managing the franchise. Bethesda did the same thing with fallout new vegas.