For the simple reason that banks are gross and Bitcoin feels amazing. We don't have to get technical to understand why this is so. Why eat chicken when you can have steak?

But in all seriousness even if the feature set seems similar to what banks can do it would only be a facsimile, as banks cannot at all replicate what lightning is doing for micro transaction sites like these. You might argue fiat banks can do a subset of what lightning can do(that is if they feel like it and don't decide to charge you a morality fine like PayPal or even worse), there is no future to it. The innovation is in lightning not fiat rails.

would you even be here if this site was built on fiat? I think the answer for everyone here would be absolutely not.