If you are willing to pay for it you can get a custom home site built in a week. It typically isn't done this way because you pay experienced people to stand around waiting for things to be ready for them to work. It is much more cost effective to schedule the plumbers for one day and the heating guys the next, then the electricians, even though each only needs about 4 hours, since it gives each plenty of slack time to recover if something takes longer than planed. Technically they can work at the same time, but plumbers go first in practice because drain pipes must go downhill, and it easier for electric to go around everything in the way than to route plumbing or heating around wires. Just in this factor we have spent a couple weeks for things that could be done in a few hours.

But isn't there still value in getting the faster build without needing to pay a premium for it?

Sometimes. The bank generally will need most of the construction time for their paperwork. Most people need to sell an existing house and that too takes time. So for the most part everyone is setup for the time it takes to build normally .