They do not have to go to trailer parks. Many local building codes allow them, and most all allow “modular” homes that are factory built, trucked to site, and lifted off the trailer and installed on real foundations, some with basements.
The only item I do not like is the plumbing and electrical. I am sure these can be upgraded, for a price, during construction. The electric crossovers are scary to me (but they meet code) and the PEX piping is not what I would choose, but it is up to code, as well.
Most manufacturers will modify any model with nearly any reasonable alternative. They can do so much more easily than on a stick-built home.
Sure, you can buy a plot of land, get the necessary permits and have a home trucked and installed on your land.
A consideration if you want something that is move-in ready.
Mine was built with glued PVC, but I would rather have the PEX. When I replace pieces I am doing it with PEX. Rigid piping and a ride on a truck don't agree well.
I knew a guy who owned a plumbing repair company...wouldn't work on 'em due to the type of piping.
The trouble with PEX is the fittings that were used for years to hold them together - a crimping ring setup that wouldn’t last long.
I have a 28X66 MH, and it is fitted with PEX.
I also have a bin full of Sharkbites - when PEX is Sharkbitten, it’s good forever.
I have been told that a lot of people are having problems with PEX because to mice, the tubing tastes like cheese.