If people stop watching a channel, even if they're subscribed, unless they have all notifications enabled for the channel, YouTube will just stop recommending it to them and notifying them about new uploads. This isn't a conspiracy; it makes a lot of sense for a recommendations engine, and it more accurately models a pattern that repeats itself time and time again: person gets big off of something popular, that something falls off a cliff, and unless they pivot and their audience pivots with them, they also fall off a cliff as their audience gets bored and stops coming back. Why should YouTube keep prioritizing and recommending videos to the people that no longer watch them?
IMO, YouTube has done a much better job recommending content from small channels the past couple years, and has introduced me to some great creators I would otherwise never have known about. Perhaps part of the recommendations have come at the expense of "channels you used to watch and maybe still would if they actually put out something fresh for a change," and there certainly is a conversation to be had there about the lack of transparency from YouTube whenever they change the algorithm, but as to which is better (subscriptions vs. small channels tangentially related to your viewing habits) is a matter of personal preference.