I think because the West (as in Cali gangs) are more about parading around with guns and when they do, shoot it is almost like a wild west shootout. Meaning mostly innocent bystanders are hit even if the target is too. So they seem more dangerous as the shootouts usually stem from drugs, encoachment on territory, or sight of different gangs. Chicago gangs do this as well but seem to do it on a mob like level. Meaning they do not want you to know what all they are into.
From my dealings here, the midwest gangs are more organized. One dude who tried to recruit me when I first got out of the miitary and came to Memphis already knew of my skill set in the service and my background out west.
To get in as a GD, I would not even have to be jumped in and would come in as a LT based on my background. He was a cool person but I had to turn him down and 8 years later I see this dude on televison already in jail but re-arrested while there for calling a hit on a deputy jailer that actually took place at his home.

Yeah they act more like the mob and rarely wear colors like out west. They give off signs like hats tilted one way or the other or tattoos of the star of david, martini glasses, or the playboy bunny or their crypted tags, but they do not openly broadcast like the Crips and Bloods and they keep their ties to Chicago once they leave.
In a sense, you can say that they are a black mafia. So much in fact that some of their "soldiers" were used a body guards at an annual HBCU football game here because attendance was down after a fight last year. This year under Vice Lord watch there were hardly any crimes, but any AA families were scared off by this show of thugs.
Another member of a Chicago based gang here is currently involved in federal investigation of two of our city councilmen taking bribes, a white car dealer money laundering and a real estate developer with a car in the gangster's name, not including the 1 or two murder charges already on the guy.
LA gangs volatile nature draws more media attention than Chicago gangs mob type ways, but from what I have witnessed these guys are more informed.
To sum it up, LA gangs are neighborhood threats, Chicago gangs are city wide threats.