Because they're worthless as parents.
That kid is lucky he HAS a parent. If they were fresh off the boat, cut them some slack. They have a 60% chance of already having HIV, so that kid probably won't make it to a ripe old age (of ~13) to use a real hand cannon like the other nogs in the USA.
I'd tell the parents if they keep yelling, they'll get a cracked skull just like their stupid bully kid. If you leave a toy you don't own alone, it's fair game. If you chase another kid, it's your own fault for getting hurt.
Same shit with the Wisconsin Dells. I recall just 15 years ago as a kid everyone was nice. Now most of the people there seem to be black or mexicant, skip in line, steal your chairs, and everything you leave on them. They're also are loud as piss, and never shut the fuck up.