That's just called having a niche. It's normal, MOST content creators who specialize in one specific thing have a hard time finding an audience when they branch out to something completely different. There is a reasonable jump between Sonic news and say, Mario news, but when Sonic content creators start making completely different content it gets less views because it's outside their target audience. That's normal for content creation and I don't think it has anything to do with the fact that it's Sonic or the Sonic fanbase. Huge creators have the luxury to do whatever they want and still get SOME views, unless their niche is games in general or they are a variety streamer like Ludwig or Jerma who specialize in just doing whatever the hell they want. Ex: if Ninja plays a random game outside his general niche of fps games, he is going to get significantly less viewers per stream, and when you only average 5-10k on your videos, it's gonna be much more noticeable when your views drop bc your view count was fairly tame to begin with. You'll hear a lot of people in streaming and YT say you need to slowly work your way into a new niche, "branching out" all of the sudden is often viewed as a poor decision. Sonictubers also generally produce quick / low effort content (I said generally), so if a Sonictuber makes ex: a COD video, its gonna be a 10-minute rant over some gameplay and is quickly gonna get drowned out by a sea of already-established COD creators doing the same thing. I'd also argue Poyo Poyo and Sakura Wars have next to nothing in common with platformers and they are also MUCH less popular series with next to no visibility, especially in the US. I like a lot of SEGA franchises because of their aesthetic and that 90's SEGA flair they used to have, but your average person who loves platformers like Sonic and Mario isn't going straight to Poyo Poyo or Sakura Wars, especially when SEGA does much less marketing for those franchises and one of them is literally a puzzle game with a very small online playerbase.