The leaked MrBeast PDF is enlightening in this regard; he knew he was building his castle in youtube and did so intentionally and explicitly because he thought it would get huge. He wasn't exactly wrong, either. His prediction-gamble earned him a life-changing amount of money.

Whether he could or should have built his castle in his own kingdom is irrelevant. His stated goal was to build a bigger youtube castle than anyone and everyone else.

> Your goal here is to make the best YOUTUBE videos possible. That’s the number one goal of this production company. It’s not to make the best produced videos. Not to make the funniest videos. Not to make the best looking videos. Not the highest quality videos.. It’s to make the best YOUTUBE videos possible.

> Youtube is the future and I believe with every fiber of my body it’s going to keep growing year over year and in 5 years Youtube will be bigger than anyone will have ever imagined and I want this channel to be at the top.

https://news.ycombinator.com/item?id=41549649

The thing with being MrBeast is that now he makes YouTube a lot of money, so they have a good reason to keep him around.