They're completely different! The similarity is at the physical/surface level only. Physical keys work in one (or rarely in several, but basically unchanging s

They're completely different! The similarity is at the physical/surface level only. Physical keys work in one (or rarely in several, but basically unchanging set of) locks, and I carry around about 2-3 of them. Hardware security keys, by contrast, work in many different places/accounts, potentially even for multiple accounts on the same service, but only after registering them there. That's not how people experience physical keys: You don't, for example, move apartments or visit a friend, and the landlord/friend "registers/adds your key for their lock". If you lose your physical key, you can't "quickly revoke it from all doors" that it locks (without kicking everybody else out).