I think the bit you are probably missing is that we live on a small crowded island, that is a highly desirable place to live. Unless you change people’s definition of a “nice home” you will never be able to build enough homes to depress prices in the way you want. There will always be someone wealthier who can buy it.
If you do manage to depress the price, nobody will want to build the houses.
House prices will come down when there isn’t someone who can buy it at the price being asked.
If you want some kind of national council house building program then I’ve nothing against that. But it will be a lot easier to make happen if you don’t destroy the value of the asset.