Two things: dividends, and significantly less covid-drop than all my other stocks.
I don't consider myself a brilliant trader (that would be Warren Buffet) but I do like a bit of the balance he preaches. Banks are indeed slow moving, but they are less likely to die away in today's rough and tumble.
Since everything is universally down right now since Covid became more of a reality than distant news, I'll happily leave a chunk of my money on shares that I know will still be worth something when I'm ready to exercise them. I have "play money" which I would refer to a pool of shares that wobble around insanely and generally make good for me, and a bunch on banks as a safe buffer. The dividends are automatically put back into shares on the bank, so I have now some fractional shares, too.
I bought the majority of my bank shares at the point I figured the banks "bottomed out" from the initial shock of Covid lockdown. I certainly wouldn't buy them when everyone is up since, as you have alluded to, it would take forever to profit on it then. Slow and steady wins that particular race. Volatile over a longer period of time is too risky if you want to "set it and forget it" and it'll make more money for you than simply leaving it in the bank.