I'm mixed hispanic and I hate them because of this game. But really it's because they're kind of in another country. Even with high speeds they're probably going to lag because the latency is too great. Players from Texas probably get good or decent connection. I am from Alabama and although I notice lag more often with these players it's USUALLY not un-bearable but it's there. At least in my experience. But I'm not one to nit pick at lag so maybe thats just me.
No offence to all the Mexicans that don't do this but another reason is that they seem to play without any kind of honour. Most of them use the cheapest tactics like revenge and quickboom and still think that the only thing that indicates skill seriously believing that they "owned" me if I die by there revenge grenade in a 3 vs 1 situation.
I know that people from all countries do that but I noticed that Mexicans do that more often.