I hate to say this, but the only way to do 'virtuous' housing is for the state to do it. The private sector is (understandably) about maximising profit. So if 6-bedroom 'executive' properties in the Greenbelt are what makes that profit, that is what they will want to build. Tbh, I don't really 'blame' them, it's what capitalists do.
There needs to be more social housing, but people won't admit it, not least because many influential people (including MPs) are raking it in from the private rental market, and living on the state's tit in the form of Housing Benefit. But that's the sort of benefit Tories like. Never mind we could provide housing more cheaply and effectively - that's an evil socialist plot.
The fundamental failure of what passes for political culture in this country is an unwillingness to admit that some things are best done by the state; others by the private sector. In particular, the private sector will always follow the money. It really doesn't care if Mr Bloggs has no house or Mrs Jones has no bus service. They should both have worked harder, that's the mantra, even if both are doing 60-hour weeks.