Most US stock of multi-family housing in low and mid-rise apartments were not built with modern building code with STC above 45 (hotel framing AKA staggered studs). Furthermore, between floors sound can carry, and even older homes can drop in STC over time depending upon the material used in insulation as well as deterioration of materials over time. My friends that lived in only high rise buildings haven't had noise issues like myself and many others where we could hear conversations on the other side of walls of neighbors similar to the extent parodied in the movie Office Space with the main character's neighbor.