As a rule, site built homes appreciate in value, if maintained. Depends on how you treat it, as with anything, but an investment as well as a home.
Modular homes (AKA: "double wides") depend on the market, quality, and setup/maintenance.
They can appreciate in value, too. Almost always, you own the land under them, too.
Mobile homes (true 'trailer houses') tend to depreciate if not extremely well maintained, depending on markets. Local zoning laws apply. It's just a tract house you can take with you. But land ownership is commonly not part of that picture, and lot rent is something that can vary wildly (especially in boom towns).
My home is site-built ca 1912. WHile that remains my home base, for half (or more) of my career, I spent my time living in temporary quarters on well sites, in about a 12X20 space at best, with the basic amenities. It was not always so 'plush'. Most of those were not trailers, but skid mounted, trucked in, and set up. They have plenty of problems compared to a site built home or any mobile home set up for long term habitation, but much of that stems from a variety of tenants and being set up for temporary housing, to be moved off in a month or two.
I have lived (main residence) in apartments and for a short while (about a year and a half, total), in trailer type mobile homes.
The only reason I can see for this push is the idea that 'you will own nothing'. Setting up a true mobile home is at the discretion of the landowner, renting the space is still paying rent, albeit it generally less than for a house or apartment of similar size, and if you have no place to put it, that asset becomes a liability, quick.