If I owned YouTube with the goal of maximizing profits, and I did not have any self imposed ethical constrains, I would focus on controlling the market of hosting videos. The technology needed to operate a video hosting is widely available and been so for the last few decades, so the only way to prevent competition and keep a market dominance would be to make sure that competitors can't compete. Keep users on the platform or else the users will end up on any number of competing platforms, splintering off the user base into more and more fragments.
With a strong market dominance one can then focus on profits with minimum risk. One way to raise profits would be to impose taxes, like with streamers get donations through "youtube bits". They could go further and demand taxes when any company do things that has monetary value, like say when a company want to make a video about their products. They could do like Facebook and many dating sites and offer a service of "promoting" users above other users. One can couple access to the site to hardware products like mobile phones, or split off features to "exclusive" access users. One can down rate the speed/quality of freeloaders, pushing users to upgrade their accounts to premium accounts.
The ways to monetize a market dominant position is to many to count. The hard problem is the iron grip needed on keeping users on the platform.