[jmprspret]

If your private SSH key is password protected, it is encrypted symmetrically with that password.

If somebody steals your password protected private key file, having the password protection there means they have to bruteforce the password. It does not 'do nothing'. Its an extra layer. If your password is secure enough, it can protect you from having the ssh private key decrypted.

[olyjohn]

It's an extra layer, but is that really another 'factor'? MFA would prevent someone with a compromised key from logging in. Password protected keys do not.

[jmprspret]

Okay I see your point now