Except for the obscurity angle of course (nobody writes exploits against Chrome-under-Docker).

To be fair, VMs are also mostly about the obscurity angle too, and if you do all your browing in a VM the cookies alone will make the attacker sufficiently happy that they will probably not care. People don't hack because they want root on the bare-metal OS, people hack because they want to steal data. If it's in a VM or container, then getting there is enough.