Pops you are purging, devouring, etc. don't take up housing or amenities. The crime/stability problems they cause made it easier to just resettle them all onto one planet. It also has one of the most insane benefits of the new population system: you get the full value of the total population being devoured but the size only goes down 1 pop at a time.
I'd be surprised if devs intended to have any planet to have the ability to host unlimited amount of undesirable pops, so I'd say enjoy it while it lasts