Because it is a relic from the past?
Bear in mind, I love relics from the past, but never for their "relevance." The Flinstones enforced patriarchal values, leaving the women to be the ones that stayed home while the big strong dumb men were the breadwinners. The show also reflects old values of what could and could not be shown on television, which meant that Pebble was born without Wilma ever being "pregnant" or giving birth, because you can't do that on television.
I'd at least give MacFarlane a shot with the show, it's a setting he obviously can use, and he could to breath life in something that was stale 30 years ago.