Because most of them are built on spec, by a builder company that doesn’t have any buyers lined up for them, and they need to squeeze them out as quickly and cheaply as they can, so that the builder can turn around and sell them as quickly as possible for maximum profit.

Of course, the people hired to do the work are intentionally pushed to cut as many corners as possible, and frequently paid criminally low wages.

Which means you tend to get younger, less experienced workers who are willing to do the back-breaking labor for really long hours per day, because they are in terror that their jobs will be gone the next day.

And you can’t keep up doing that kind of heavy labor for those kinds of hours for long. You age out rapidly from that kind of a job. And then you get replaced by a younger and cheaper and much less experienced version of you.

Cheaper houses allow more people to own houses. Wood frame houses take less wood than full timber houses, and are safer in a earth quake or hurricane than stone or brick.