But compartmentalization does mean that barring a hypervisor exploit, each exploit can potentially be prevented from affecting more than a small part of the system.
I care a whole lot less if Chrome is exploited if it can't access my ssh keys, for example (not that I wouldn't still care, but the potential damage would be limited).
Edit: But the way you talk to me, obviously I must be stupid.
Compared to the few hundred lines in the hypervisor providing VM-level isolation you'd be a bit mad to say that these are equivalent means of isolation.