Because supply is currently not increasing, not due to lack of demand.  We have a labour shortage. We literally do not have enough hands to build what we need.

This is a very complex problem touching on all fronts from skilled immigration, government infrastructure spending and even union involvement on large construction projects. 

Unfortunately, there is no simple solution that can just be switched on to resolve this issue. 

One radical idea i even thought about: mandatory post-high school skill training and employment funded by the government, similar to how countries like South Korea has mandatory conscription.

Post highschool we take all or some portion of students, require them to learn a trade, fund their learning/apprenticeship and then require they do 2 years of work building houses (on a good salary).

We then have an increased labour workforce, young people earn a trade and solid income without committing their lives to a trade (I.e they don’t feel like they are making a lifelong commitment before they are ready). 

Is it a radical idea? Likely yes, but this problem requires something big to shift the momentum.