I know a few folks who do full time between things like SynAck and BugCrowd. SynAck is the ideal model in my opinion for pivoting to full time vs part time as a professional bug bounty individual, although it takes a ton of skill and hardwork. I'd say it's the exception moreso than the norm.

If you are interested in learning more about SynAck and it's model shoot me an email: i@willcode.it I can try and setup some contacts from their side that are working full time on platforms like it