It’s all to do with where they are being built.
Low cost housing only exists in some areas, and not in the South East at all, but there are well paid jobs in this area of the UK so ‘grandchildren’ here would be able to get on the housing ladder eventually, especially when two salaries are taken into account.
There is a crisis because the population has grown here too quickly, many doing low paid work yet still requiring housing, usually in the rented sector.
Add to that the break up of marriages / partnerships, and it’s easy to see why we don’t have enough housing.