Gamblers use bitcoin for not giving any identification document and can do gambling in any age, online job seekers use bitcoin as payment for job, so their are so many ways for people to use bitcoin.
Those are already why people are using bitcoins not why they should use bitcoins. Btw, online job seekers usually use Paypal because it's much easier to use if you're not tech savvy since you just link your bank account and then issue a payout.
Once you deposit money in banks the money is not your anymore. You are giving the money to your bank with a promise they will give you back anytime you want. People are interested to use bitcoin to have a complete control over their money, without the limitations banks have
That's also another way to look at online wallets that don't give out private keys. There's no contract or anything that has happened between the online wallet and you. Once you deposit money, and then they stop paying out people, you will be begging them to give your very own money. Use desktop wallet so you get full access to your wallet, everyone.