Maybe the Hopscotch Team decided to change the channels. They often do it to suit the Community, for example they added #pixelart when people were making a lot of pixel art. Maybe they decided some channels weren't really being used so they removed them?
There different channels I've only seen those before
Like @t1 said, I think that they become, somewhat useless, like less people were using them. The very few times I went to the #minecraft tab, most of the projects were spammy and were out of topic.