Well one was in NYC and the other in Sydney. NSW has a strict building code that requires acoustic testing (literally hitting the structure with a hammer and ensuring no sound passes through).

I lived previously in a 100yr old brick walkup building in NYC. It was like my neighbors were all roommates in one house. That apartment almost drove me insane with the amount of neighbour noise I would hear at all times.

Concrete really is such a fantastic building material and yet people want to build their houses out of timber for some reason.