"Homes", not "houses".
Saying you want to build (or want to "see" ) however many hundreds of thousands of new homes is all good and well, but the problems come when you try to find somewhere to build them, and building the infrastructure to support them.
An alternative solution might be to reduce the amount of people, however this might involve curbing immigration (controversial), discouraging people who can't support children from having them in the first place (controversial), or encouraging people to downsize to a property that is only as large as they need (controversial).
Simply building an unrealistic amount of new properties seems to be the least controversial way of solving a problem which many seem unprepared to accept exists.
It seems to me less of a case of which party is the most ambitious, more which are the biggest liars.