Someone else touched on it but mobile home parks can actually be very exploitative because the home isn't actually mobile, it can generally never be moved again, but the owner has no claim to the land. So it's all the downsides of owning a home AND renting with literally none of the upsides. The home doesn't appreciate, and you have no control over your future payment, and can even be evicted from your home that you own outright. Without some change there, they are not a solution.
To your point though, building housing developments organized like mobile homes could be viable, however if you're going to use up that much land you really should also build vertically to make the most of it. But then you get into the same issues we have now, building up costs a lot more, no longer stays affordable, etc.