We don't have a huge mugging problem. We have muggings (I've been mugged), but they occur infrequently enough that society isn't disrupted. You can't say that about ransomware. Not only that, but we have done things to defang muggings; for instance, it's been made less lucrative (and more dangerous for the mugger) to steal a modern phone.
I'd argue that's a small part of the reason. Like a rounding error vs the inconvenience factor of dealing with stuff like coins, having to go to a physical location during restrictive hours/days to obtain more than a trivial amount of cash, etc.
