This isn't true. Open up Preferences, go to the Advanced tab, and there's a checkbox "Allow creation of vaults outside of 1Password accounts". Check this and you can create local vaults again.
I believe it's disabled by default for 2 reasons:
1. Simplicity. Most people who use the subscription service don't want local vaults, because they won't be synced or available on the web (or subject to administrative controls). By disabling local vaults, you can't accidentally create one.
2. Once you re-enable local vaults, you have a local Primary vault and unlocking that is how you unlock 1Password on this computer. This is a potential point of confusion, because you'll be using a different password now than your 1Password Account password, which comes back to the simplicity angle.
I believe it's disabled by default for 2 reasons:
1. Simplicity. Most people who use the subscription service don't want local vaults, because they won't be synced or available on the web (or subject to administrative controls). By disabling local vaults, you can't accidentally create one.
2. Once you re-enable local vaults, you have a local Primary vault and unlocking that is how you unlock 1Password on this computer. This is a potential point of confusion, because you'll be using a different password now than your 1Password Account password, which comes back to the simplicity angle.