This is from talking to builder agents out here. They maintain a waiting list of interested buyers and when a spec home has been started they give the first person on the list the first chance to purchase it at the builder’s price. If there are any options at all it is just paint and flooring- everything else has been determined by the builder.

If the person passes on the home they are dropped to the bottom of the list and the home is then offered to the next in line, and so on.

They are doing this to speed up build times and help keep costs in check.