People should use it because there are many reason why they should use it.
First reason if they need money just earned here in bitcoin by buying at low sell at high.
Second reason if they want to transact anonymously they should use bitcoin.
Third if they want to earn more money with many different ways use bitcoin.
1)Bitcoin price is rarely dropped nor increased that high, so buying and selling bitcoin is pretty hard to be profitable.
2)Bitcoin is pretty anonymous, but not fully anonymous. You could still got traced, but it's hard to do that.
3)You still could earn money by fiat, not only bitcoin. It's even easier using fiat for getting jobs.