Because of the way the animals behaved after he was acquitted. Cops across the country said to hell with it. They will only go to a problem if called out to handle one, but they will not put forth any proactive effort. If they see a drug deal going down, they just ignore it. If they see some black guy crash a light and almost kill a pedestrian, look the other way. If they see a known convicted criminal in the area that has evidence of a gun being on his person, pretend you didn't see it.
It happened all across the country, so don't say it didn't happen there.
It didn't happen anywhere... None of those things have anything to do with murder.
"Oh noes, we'd better not hassle black people anymore!"
Wow. That's terrible. You mean you have to treat them like white people now? Oh my God.
Nope, there wasn't a Furgeson effect or even a van Dyke effect. What there was was a huge influx of new guns, combined with- unfortunately, turf wars over the drug trade by smaller gangs after the Feds busted up the bigger gangs in the Oughts.
The other part of the problem, of course, is that the community no longer trusts the Chicago PD. It happens after you have incidents like the mentally ill man who called for help, and some thug ass cop shot him, and some lady who happened to be behind him.
Oh, this guy didn't go to jail. Didn't go to jail when he beat the shit out of someone in a bar.