So, with most password managers, when you authenticate on a new device, you are prompted for MFA. The user had a keylogger installed on their machine, so the attacker could collect the master password, but how did they login to the vault on a new machine without MFA? Did they get the MFA seed and login on a different machine, and nobody received a "You're using LastPass on a new machine, if this wasn't you..." messag…
The 2FA part in the password managers (and least in the major players currently) is to get a copy of the encrypted vault from the server. The user did that part, and the encrypted vault was not easily accessible locally.