One issue is where do you build them? areas like the South East that needs a lot of new housing tend to have very few available sites and when building does go ahead, they tend to build retirement homes rather than low cost housing to help those struggling to get onto the housing ladder.
Then...
Surely it's just down to simple economics, wages go down when there is more Labour available to takes these roles and businesses aren't facing much competition for employees.
Wages go up when there is a shortage of Labour for a role and therefore employers have to pay more to get someone to...