This has been a phenomenon for the better part of a decade. I can't even remember when it happened, but some day they decided that the channels one was subscrib

This has been a phenomenon for the better part of a decade. I can't even remember when it happened, but some day they decided that the channels one was subscribed to were less important than "hot videos". They also split and moved those subscriptions into some sidebar where you had to click on every subscription manually to see what was new. Their focus is ads. Top videos mean ads are watched more often so that's what they promote. Everything is geared that way and creating bigger, less heterogeneous groups means there are less "niche" videos. I'm sure their AI has worked out the smallest number of groups that spans the biggest amount of users and drives views upwards that way. If you don't want to get caught in the pooptube loop, don't subscribe, don't create an account and get recommendations offsite. They are more likely more diverse. In fact, if you want new stuff, don't go on youtube, go to vimeo, peertube, dtube, or whatever else has tube appended to its name.