Well 100 years ago there was much less public involvement in construction. If you wanted to build a residential building you could if you owned the land. The neighbors couldn’t stop you because they didn’t like your project. Nowadays, with planning commissions and zoning laws there are a lot more obstacles in the way for creating new housing. Not saying getting rid of these public regulations is a good idea, but just pointing it out.

Also, construction was much cheaper back in the day. People could live in smaller spaces with more residents. Now, the avg square footage per resident is much higher. People expect more space. A house that used the fit a family is now deemed “too small for more than 2 people”. Residential units could also be built more cheaply then as construction standards were not as high and they didn’t need as many features/amenities as they do now (multiple bathrooms, more electrical outlets, etc.) And without OSHA and modern pay requirements labor was nowhere near as expensive as it is today.

But leaving these modern requirements in housing aside, we can still provide enough housing for everyone if we get held back by restricting new development.