What are the circumstances that allow this behaviour from companies? It's a more complicated question than just "Why are companies behaving this way", that's easy. Greed, mostly, and because they can get away with it. I'm more interested in why they can get away with it. Too few, or unenforceable regulations? Too many available workers? Too many qualified or overqualified people fighting for too few jobs?
Honestly it's fine to not want a career, but you can't do nothing. We rely on people's work to get materials, build and heat homes, grow and distribute food. Society is built upon contribution. A UBI is not the answer because that's still just other people's labour. You cannot have both an opt-in working class and an opt-in nonworking class and have a healthy society.