Well, that and those who lose nothing but have a chance to gain quite a lot.
Pretend you're a foreigner with a shitload of money and connections. You hate Americans, you only value power and you have no problem spilling blood to get what you want. So one day you find out that the US borders are completely open, guards aren't giving a single shit about stopping people from hopping the border. And what luck, one of the places right past the border is highly populated with foreigners from all over and the authorities in charge are either lazy, incompetent or only answer to money. The area is willing to sell land to foreign investors and shit, it's right near the ports too! The only thing stopping you from buying a bunch of property is that it's already been claimed and shit's retarded expensive. So you hire a crew of motherfuckers to go hop the border and wait for the right moment to give them a signal to go torch some shit, specifically in nice areas populated by locals. Once a couple of blocks are gone, now all of that real estate is up for sale for pennies on the dollar. The city takes the blame for everything and becomes so desperate for funding that they'll let you buy as much as you can afford, at that point the only ones who will get in your way are other foreigners that are thinking the same thing, unless it becomes a group effort.
I know this sounds schizo as fuck, but I remember when Xi visited San Fransisco that one year and Newsom acted FAST to get the city cleaned up for Xi's arrival so well that it was hardly recognizable with how pleasant it looked. He made that happen over the weekend, it's not like he's unable to get things handled. But with LA, he pretty much let it go to shit. There has to be SOME reason.