The idea is that virtualization escape vulnerabilities are quite frequent. An attacker might not have one on hand at any given moment and you might patch your s

The idea is that virtualization escape vulnerabilities are quite frequent. An attacker might not have one on hand at any given moment and you might patch your system frequently when they become known. But this only means a determinated attacker that has emulated root needs only patience. Good security always means stacked independent layers, betting the farm only on the guarantees of your VM is very unsafe.