YouTube is too lucrative of a platform to pass up. It's not just hosting, but literally sending droves of viewers their way, and making sure those viewers are paying to watch in a way that enables those creators to earn a living. Take any large creator and 95-100% of their regular fanbase probably wouldn't follow them to another platform (unless it's so big that all/most of their favorite creators also go to the same platform).
Any other platform not only needs to offer cheap/free video hosting, but also send tons of users content similar to their interests in a way that enables new and up-and-coming creators to grow, and it needs to provide a way to pay out those creators, or there's a negative incentive to send any viewers to the other platform that strictly makes them no money.
Plenty of creators upload their things both to YouTube and Nebula, and I choose Nebula for the ones that do. The app isn't perfect, but it gets the job done.
