Homes in greater Boston are definitely not all or even mostly up to code now. My old ~1900 greater Boston apartment still had live knob-and-tube wiring. Fortunately the 1880 home I own now was thoroughly rewired and now more or less in line with the electric code, although it’s still far from modern building code in other domains (plumbing, rafter spacing, insulation, stair rise/run, list goes on).
In some important ways quality was due to the availability of materials, but cheap labor played a big role too. Many building practices before WWII were extremely labor-intensive compared to today. Lathe and plaster walls, knob and tube, board sheathing, fieldstone/rubble foundations, mortise door hardware, etc.
My 1850 triple-decker has code compliant electrical and plumbing, egresses, common area lighting and dual exits. Definitely not accessible and the stairs are typical for the era— the last big brick building I lived in that was built around 1900 was super solid but the stairs were murder— like 7" treads and it was a 4th floor walkup.
In some important ways quality was due to the availability of materials, but cheap labor played a big role too. Many building practices before WWII were extremely labor-intensive compared to today. Lathe and plaster walls, knob and tube, board sheathing, fieldstone/rubble foundations, mortise door hardware, etc.