What? Revolvers are really common. They're incredibly reliable, in a way that a semi auto mag fed pistol isn't.
A revolver rotates the cylinder and the hammer falls on each individual round. If the ammo is bad (incredibly rare but it happens) then nothing happens, but just pull the trigger again and you're not jammed or anything.
A mag-fed semi auto, while higher capacity, has WAY more complicated moving parts. There's tons of ways it can jam up or malfunction, and since all the ammo is stacked in the same spring-tensioned magazine, if there's a problem you have to clear the jam in order to fire anything else.
If you're in a position where you are actually pulling the trigger your fine motor skills are gone because of adrenaline. Clearing a jam like that isn't something you'll be able to do effectively without a ton of training, and most people don't have that kind of training.
So a lot of people prefer a revolver. It's only 6 shots instead of 11, 17, whatever, but you KNOW you'll get six shots, and the thinking is if that's not enough then 17 probably isn't either. It's personal preference.
But yeah, they're not just "grandfather" guns.