I blame NIMBYism, at least for older multi-family. (Shoddy SFH with poor noise insulation is a different story.) If zoning were more relaxed, we would be tearing down 100+ year old multifamily in places like Massachusetts and putting in new homes with modern sound proofing between tenants.
Based on empirical data, new buildings, as they relate to multifamily dwellings, have little to no sound insulation. Older buildings are probably better in that regard.
