There are actually quite a few places where they buy bunkers - but with luxury and stuff. it's also marketed as a way of safe spot to retreat when the surface goes bad.

obviously, it's rather a big ,"we found a way to make money out of rich peoples fears and doubts" rather than actual security measures. if things really go bad, how are they going to know, that their security guards aren't going to ditch them? and if they isolate, then they cannot sustain their lifestyle in a bunker with bunker food.