Because of logistics, they can only build a certain number of houses with the resources they have. You guys seem to think houses could be built like it's a production line in a factory. They are not purposely limiting the number of house they can build, they only have a certain number of skilled workers who can get the job done so they are limited by that. And at the same time those home builders are the ones who owns the lands that are zoned for new housing and they aren't going to let some other company build on their property and make the lions share of the profit . Say I build 100 houses a year and I want to double that to 200, where are the skilled workers to achieve that?
Before a single house is built you need to lay down the infrastructure to support said houses. First they do the sewers systems, water supply, electrical and gas line feeds, that alone could take 2 years and if they wanted to double their production where are the skilled workers to do that? Then it has to be inspected by the city and pass so they can pour the concrete foundations and that has to be inspected and pass. Then they build the frame, roof and brick the house, all skilled workers that can't be easily replaced. Then the electricians, plumbers and HVAC guys come in and do their thing and that has to be inspected, again all skilled workers. From there they put up the walls and drywall taping, tile the bathrooms, install the washroom fixtures and finish up by installing the electrical outlets, lights. Then they do the flooring and painting.
When the younger generations aren't interested in doing manual labour, please tell me where you find the manpower to build more house in a short time? I know your answer is going to be immigrants, but please tell me, do those immigrants have skills and knowledge to do electrical, plumbing or HVAC? No they don't.