My experience as someone who loves drawing and does often delightedly remind herself that her day job is sitting around a park drawing shit:

basically, yes, all of these reasons apply.

I'm good at drawing, not at selling myself; my work sells itself to a certain degree but that only gets you so far. Not everything I'm paid to draw is a thing I love to draw, either. And sometimes even a thing I love to draw becomes less fun when it has to meet someone else's approval; going back and forth with a client is a very different feeling than "I start drawing and I fix things I don't like until I'm happy with the piece".

Deadlines suck and I mostly arrange my work so as not to have any. Yes, this is a luxury. It probably means less money but I make enough to get by.