After powering on laptops and desktop computers, you are allowed to use biometrics for login. But, as far as I know, biometrics are not allowed for unlocking phones after powering them on. You are only allowed to use biometrics after you've first unlocked the phone with a PIN/password.
Passwords or even PINs can be used to derive a decryption key, which is important if a device's storage encryption is to be really secure. You can configure PCs this way too, requiring a password to decrypt the OS drive before booting. It's not, as far as I know, currently possible to reliably derive a secure cryptographic key from a fingerprint or other easily-measured biometric (and if it were, anybody who could scan the relevant biometric from you could probably derive the key themselves).
Login security on PCs is less based around "be secure if the device is stolen or physically tampered with", and more around "be secure against a network attack or a random user walking up to the interactive terminal". Phones rarely run network servers in the background, and while they can be stolen easily, they're less likely to be attacked by a random person wandering past your office while you're away. Indeed, until pretty recently, the assumption was that, if a talented attacker got unfettered access to a PC, they could get everything. Thanks to strong full-volume encryption, that's no longer true, but that happens long before the user sees an OS login screen.
With that said, biometrics of any sort found in commodity devices are definitely less secure than a good password. Of course, good passwords are inconvenient - especially on a phone - and people are bad at generating and using them (for example, a password you've used anywhere else is no longer a good password, and people reuse passwords all the time). Thus, phones strongly encourage the use of biometrics, while most PCs still ship without the capable hardware and many corporate policies disable the use of biometrics even when the hardware is present.
