The first reason is that big profits can be booked,as we have far more buyers than sellers.
The second reason is it is cheap money that is lifting house prices [not higher wages.]
The third reason is low rates will not last for more than a few more months or years.
The fourth reason is when you want to sell the market will not want your shares.
The fifth reason is it will be the fear of rate rises that will start the slump in housebuilders shares..This could come out of the blue at any time.
The City thinks that these stocks are cheap as turnover and prices are going one way[up] helped by cheap land bought by the builders in the last 3 years.
I take the view that just as production steps up a gear, with higher wages,and material costs to boot, lending costs will jump.
When the cost of money doubles [from a very, very, low base], the fun stops dead.