Everything that has a store requires an account.
- Steam - you need Steam account (also applies to Valve Index then)
- iPhone - you need Apple account
- Android phones - you need Google account
- Oculus before - you needed an Oculus account
The short time during which they required a Facebook account (i.e. an account linked to an unrelated service) was a fuck-up, but they have since reversed that decision. Now it's just a separate standalone VR-related account.
If anything, that is still better than the current Google/Apple situation with their accounts, which link together a bunch of unrelated services (photos, email, payments, storage sync, etc.) in an inseparable way.