If a stealer gets one of my keys, he doesn’t get access to everything (especially email which is the most sensitive).
And also, if he manages to get the keys, he will need time to find which key is bound to what, it will help me delete the key.
And if a key is stolen, it will be faster to make it useless.
The goal would be to use keys from multiple manufacturer but still having the master key at home.
And also I don’t know if keys have a limited amount of accounts for FIDO