Because, as shown by SGX, it doesn’t work. And if it did work, it would lead to a whole new magnitude of the malware problem - malware protected from you by hardware.
The right way to do it is the other way round: have a trusted hypervisor and run your untrusted OS in it. See TrustZone for example.
The right way to do it is the other way round: have a trusted hypervisor and run your untrusted OS in it. See TrustZone for example.