Lots of things in different ways, but for one example, ad & premium money from videos that they demonetize.

Not to mention literally stealing original content and granting it to anyone else who simply claims copyright without proving it or being able to prove it since it's not theirs.

Then there are all kinds of indirect ways as a consequence of their various policies and how they implement and enforce them, like showing me ads after taking my premium money, or collecting and selling the profiling data of my watch/like/dislike data, etc.