A Youtube search for Sonic Robo Blast 2 still shows a lot of videos being uploaded regarding the game itself. The only difference is some of the big Sonic tubers are covering other fan games and mods to official titles at the moment.
Once we see big new characters or map packs coming out more often, then activity will pick up, but progress on such has gotten slower in part due to larger and more detailed levels resulting from what the development of the game allows now.