It can be easier to run a jail (or container) and assign it an IP and run standard applications with standard configs than to run a second instance of something in a weird directory listening in a special way.

The other big difference between this and a VM is that timekeeping just works.

You're not necessarily restricted to friendly-only tenants, either. Depending on how you configure it, there can be pretty good isolation between the inside and the outside and the other insides. You lose a layer of isolation, but it's not impossible to escape a virtual machine either.