Even if my laptop is unlocked, each 1Password interaction needs my fingerprint. That unlocks a secret stored in the Secure Enclave, which I trust. (Security is hard and flaws are possible, but Apple has done a reasonably good job here from what I can tell.) I only have to mess around with typing a long string of nonsense in when I'm registering a new device, rather than every time I want to use my SSH or GPG key (or trusting an agent to hold it in memory, which... I'll do it, but I won't like it).
I wish I could rely on similar things from Linux, but the user experience just isn't there on the desktop. A previous employer issued laptops that had both a fingerprint reader and some kind of HSM, so the hardware was there, but I remember both of them missing drivers at the time, and even with drivers the userland software support would've been very hacky.
[0]: https://support.1password.com/touch-id-apple-watch-security-...
When you enable the PIN, you deliberately weaken your security for convenience. However, when the database unloads, your database is still protected by your pass phrase.
This is not the case if you disable the "lock with master password on restart" option. In that case only your PIN is guarding access the the vault data.
Using a PIN shouldn't have to mean weakening the security, since there's several secure implementation options of a PIN. (See other comments about Windows Hello for example)
That's why SSH keys or GPG keys are typically protected by a pass phrase. Not a PIN, not a password, a pass phrase. At least that's the wording that OpenSSH uses, and Bitwarden should do the same. Secure your database with a pass phrase, not a PIN, or else you might be vulnerable. That's how it should be communicated to the user. These details matter.