Zoning laws (minimum lot sizes, minimum setbacks, minimum parking requirements that are uneconomical to meet on a small lot, bans on 2- or 3-family houses, etc) have intentionally outlawed many smaller, more-affordable styles of houses since 1970, so new houses have gotten bigger.

This is often what's missing in the discussions I see on facebook among people that have no knowledge of real estate. "My parents bought a house that they paid off in 5 years on his meager salary!" Well yeah, but it was half the size of your apartment, Susan.

This should absolutely be talked about more often.

Where can I buy an affordable new 700-1200 square foot fee-simple townhouse on a small urban lot with no parking because I don't have a car? They're illegal to build in almost all American cities, but a huge component of Japan's housing stock.

Get one with a garage, and turn the garage into an office.

Typical Northern California architecture, which includes a garage that most people don't park their car in, provides a lot of spaces to start projects in. It's better to start a project in a garage than in a spare bedroom or basement, because if your project starts taking off you can have customers and employees there without awkwardness.

It only works if the climate is good enough to work in a sheltered but unheated space year round.

That's a good point. But a 2.5X increase in house sizes doesn't account for the 100X rise in house prices.

If a house cost $2000 in 1950, it probably costs $200K now. It can't all be due to increase in house size.

The biggest culprits probably are tax incentives for homeownership, increased population, zoning laws limiting housing development and international investment tied to citizenship attainment.

It's worth noting that square footage is not the only metric that houses have increased by.

Houses have more amenities (e.g. central air). Houses have more volume via higher ceilings; 30 or 40 foot foyers were mostly for the unbelievably rich before McMansions. How big are lawns? The garage? And so on.

I don't think it's everything, but it's not insignificant.