It has to do with mass media, which is by no means progressive. My step-daughter adopts black slang because it is used by the mass media and hence by her friends. They have no idea the history or meaning, but it is defined as cool by marketers (note: not progressives) who want to sell things. So they adopt it. I suspect much of the blogsphere, being fairly young, adopts it for the same reason.

I will point out, however, that you are probably missing the point in this particular case. The link to the sex industry is an intentional reference when people use "pimping" in regards to advertising in much the same way people intend the peripheral implications when they refer to "raping the land." Still, the adoption of slang by people who have little clue what it means is pretty irritating. But so can be someone who misses the point of particular cases where the adoption is done with full knowledge of the implications.