There is a mobile home park that I drive by occasionally, most of the people I see are Hispanic. Fair number of pretty nice vehicles parked next to beat to hell mobile homes.
Think about it a little, you can't buy a real home, land registry, taxes, mortgages, nosy neighbours ETC. Hence living some were cheap you have realtifly speaking masses of disposable income. Small personal goods get nicked, but your cars sorta a safe haven. Its a completely different life style and what does not make sense based on yours does there.
Its also worth remembering whilst most of them don't get a very high hourly rate, with no taxes, they will all work long long hours, hence they still have a decent total income after basic living cost.
One of my ex employers was big on illegals, we ended up being raided, was the quietest i have ever heard the place, 2/3rds+ the people there disappeared into the fields - woods in seconds, so many grinders - machines spooling down suddenly and all at once it was spooky. Immigration were the biggest bunch of clowns going, all us remaining true brits got read our rights, i tried to convince em i was from some were warm tropical and sunny, but they were not having it, my Jamaican ascent just was not good enough and apparently no Jamaican could be that white and pale :-(!! Hence instead of being deported some were nice i got left there in the cold :-(
My experience, 99% of illegals just want to live some were safe, raise - support a family and get on with life. There more than happy to work hard to achieve that. Like in most fringes of society, its a great place to hide if your upto no good! Weather that be drug peddling or terrorist based.
As to the whole Mexican - America border wall thing, IMHO your disillusion if you think it will work. If you truly want to address the drug problems, the terrorism problems, you need look a lot deeper and fix why a significant chunk of society is so broken. A wall won't stop it. Will just make every drug a bit more expensive!