YouTube wants you to keep coming back for more. It's understandable for any service, but more so for one that capitalizes on you watching videos daily and finding more compelling and interesting content all the time. YouTube's homepage often guesses what you're interested in watching (and at least for me, it gets it right), combining new videos from channels you already subscribe to with videos similar to ones you've already seen and timely content you're likely interested in. Many of the latter two usually come from channels you don't subscribe to, but you may want to do that. And now YouTube is starting to nudge you in that direction.