It's not even about the law, we just don't put kitchens or showers in commercial buildings, and retrofitting them in would be extremely impractical.

It's not impractical to tear down a house and put down a perfectly building code compliant apartment building.

Would love to see this argument quantified.

No, you wouldn't; it's been quantified for you on this thread, and you ignored it.

Noted and refuted.