I think their best answer is a sort of blacklist system where if Intel becomes aware one of their key has leaked, their servers could stop telling people it is genuine (this gets into the details of EPID and DCAP that I really don't want to clutter my memory with, so my retelling may be less accurate there)
To prevent the idea with fake certificates, I think you "simply" pin some Intel root certs in your enclave. Do TLS with those, verify the "TCB" cert chain with them too. Then the VM either lets you run on a real CPU and cannot poke your encrypted memory, or it emulates you and this is back to the previous scenario (it owns you locally, but remote attestation fails)
The whole thing that makes SGX interesting and not a boring traditional HSM is remote attestation for secret provisioning, sealing of secrets, etc. This means you in theory run workloads on someone else's computer without having to trust it. If your secrets are already on the attacker-controlled VM and you only verify things locally, this is useless. Nothing can save you, the VM already owns your entire environment.