I built a neighborhood of affordable homes for our community land trust a few years back. We used factory-built homes and brought them over the ocean and installed them. They were built to UBC standards, fully engineered, and likely of higher quality than on-site-built homes. Still, we got a lot of pushback from the county who didn't at the time understand the difference between an RV and a modular home built in a factory and installed.
It was a huge time and money saver to do the project this way - the homes arrived on the very day promised in the contract, they bolted right onto the foundations we had prepared, and the buyers didn't have to float construction loans for nearly that long.