It's pretty straightforward - zoning interferes with labor mobility and thus interstate labor markets. If programmers outside of SF cannot afford to buy a house

It's pretty straightforward - zoning interferes with labor mobility and thus interstate labor markets. If programmers outside of SF cannot afford to buy a house in SF, it affects their wages by suppressing their ability to move when they cannot get a high enough wage locally. There's precedent in intrastate agriculture being subject to the interstate commerce clause for similar reasons (that is, affecting interstate prices)