According to this documentary its thanks to Earl Butz and the Farm Bill of 1973.
Beef these days comes from subsidized corn with little (nutritional) value but to make food cheaper for americans. add that to the being a huge percentage of what our USDA beef is fed in their huge animal confinement facilities, it makes the quality of beef cheap and substantially fatty compared to grazing cows (and pink slimy apparently). on top of that these
cows never would survive on this feed if it weren't for the mercy of the slaughterhouse, they need to be juiced up with hormones and anitbodies so they can even live that long. but hey, the american family's percentage of their income spent on food has never been lower, thanks to government subsidized corn.
King KORN!!. If you don't think "cheap" and "more" are two words valued (subsidized) by the USDA, seek the words of
Earl Butz.