Do you know why some builders may reduce price to build?

He may still have land liability that he acquired before the slump. He may used borrowed money to acquire these lands. If that's the case, even if he has no inventory to liquidate, his land is eating him away, so he has to finish the project even if he may lose on the structure profit.

Many other builders don't secure land in advance, they simply bought option contract to buy the land at a set price within a time period. If the market is good, they will exercise the option to acquire the land. If no good, they will give up the contract, losing only the option premiums. Thus, each builders are different. Big builders usually use land options, so they are better off than smaller builders who has to buy the land because they lower buying power.

I agree that if a builder deem it profitable to build at a reduced price, they may go ahead and continue to build. But nowadays the land price is so high. This limited the amount of builder reduction in price.