it’s that there’s not enough space to accommodate everyone so it’s not financially realistic to most people who want to.

There’s plenty of space, it’s used incredibly poorly due to free parking, zoning regulations, and running highways through cities. The financial component is simply there aren’t enough of these spaces and they aren’t dense enough (and they could stand to include a lot more public and social housing, but people oppose it because they don’t want “those” people in their neighborhoods).

That’s not to say that reforming suburbs to make them more livable wouldn’t be a part of the solution too.