Because their algorithm is pretty damn good at recommending relevant stuff. For example, titanfall 2 got revived and I found a lot of small youtubers (<20k subs) making some incredibly good content through it. The secret is to click "not interested" on all the clickbait crap often enough and at some point it'll learn.

Though I do use on an android TV and block out crap like shorts altogether because google's youtube app is unusable.