If you create resources outside of terraform/CF your doing it wrong. This is a feature, not a bug.
On the other hand I hear that CF's rollback is better at not leaving things in a busted state.
If we followed the (patently poor) advice above, CF users would not have been able to use NAT Gateways - to take one of several prominent examples - for many months following their launch. Terraform was substantially faster to support them, but being able to import resources created outside the normal mechanism for _any_ reason is an essential part of any IaC tool.
But at least you're doing it!
There are sometimes holes in Terraform coverage.