Want to know the real reason? believe it or not, like many things it comes down to one simple thing: Money
After the economic gains of the 1980s (you know, that "awful" period of evil "Reaganomics" and "trickle down"), minority groups in America had more wealth and spending power than any other time in history.
Meanwhile, hundreds of independent media groups were being bought out by one of six mega-corporations, all of whom used the same marketing practices. They rushed to profit off this growing minority affluence by creating programming specifically aimed at them.
Many people today forget that FOX, in its fledgling years, gained a foothold against the "Big Three" by launching programs featuring mostly-black performers ("In Living Color"..."Roc"...etc.). At the same time, networks wanted to appeal to the maturing 1960s Boomers "counter-culture" mentality with "anti-traditional" shows like "Married with Children"...the era of the idiot father, insecure mother and snarky kids was born...
The mid to late 1990s became a time when all things non-white and non-traditional were pushed in the media...culminating with Michael Moore's "Stupid White Men" in 2001... Although some may say this is a good thing, understand that it was all driven by a few networks looking to exploit new affluent audiences.