Pre-sales always include broad sweeping allowances for variances in final cost; for instance, folks who pre-bought condos two or three years ago are just starting to get sticker shock now that the final price has hit them, thanks to skyrocketing materials cost. The price they agreed to pay, with those variances they agreed to.

Without the assurance that someone else would shoulder the risk the builders would have walked away. Like they do in China, and where they have to demolish half finished towers because the builders dropped out and none will take it on.