… Wait, what? I mean, possibly if you’re a large investment bank , those can be quite profitable (until they’re abruptly not; see 2008). Retail banks (which the ‘be your own bank’ people are presumably referring to; if you want to be your own investment bank you can just skip the ‘bank’ bit) are generally not particularly profitable.

Being a stable working bank is really really hard. Most people don't have the knowledge, time or desire to do that.

For 99+ % of the world's population using fiat currency is simple and the learning curve is basic school maths.