Are we forgetting that for most users SL is a 'hobby' or a 'hobby job' and for most it's not a full time career.
Supply and demand controls pricing in SL just like in RL, if a creator wants to earn a RL wage, they can just price their items accordingly.
If the DJ wasn't happy with 8000L$ from tips, then they don't have to do it, it's the beauty of choice.