Tbh, I suspect the only reason we don't have more people living in US-style trailer parks in the UK is because of the association here with that kind of static caravan/mobile home and travellers/Roma.
I suspect that if it wasn't for anti-traveller/Roma racism, NIMBYism and authorities not wanting to grant permission to such sites, we'd probably have a lot more poor people living in British 'trailer parks'.
As it stands, many 'park homes' aren't an option for permanent homes, because of planning consents, in that many park home sites have restrictions that you can't live on them year round, you can only live there for eg 11 months out of every year. So their deliberately intended to be holiday homes rather than permanent homes.
In some respects, it's bad that such bad attitudes prevent poorer people from accessing more affordable homes, the way people can in the US, because of such prejudices. But then again, maybe it's better that authorities don't create lots of trailer parks and we don't have lots of American-style trailer parks and people permanently living in caravans here?