Why aren’t bathrooms soundproof?

Now I get that there are old houses or smaller places, but overall most bathrooms have no soundproofing (might even be echoing a bit) and you can hear a lot without even without trying.

I don’t really get that. Nobody in there wants anyone on the outside to hear what’s going on if they are blowing up the bathroom, and nobody on the outside wants to listen to someone blow up the bathroom.

I feel like it would be a pretty good selling point, cause there would be at least a sizable community interested in paying a little extra for a soundproof bathroom.