The official explanation from FOX was, that the spectator getting less and less. That was enough that the longest running sitcom was taped the last time
at the 5th may. And that even though FOX got well known through MWC.

But it was clear, when FOX changed the timetable and sended MWC at Saturday night. After they recognized that this wasn't so good they
put MWC back to sonday afternoon. But it was too late.
FOX did't get enough money with the sitcom. We have to remember that the actors earned a lot.
Ed O'Neill had been the best paid actor ever been in a sitcomarsteller gewesen sein.

And here ist the Terry Rakolta part

Then in 1989, a Detroit housewife named Terry Rakolta started a campaign to convince advertisers to boycott the show. "I find it very offensive." she said at the time. "It exploits women, it stereotypes poor people, it has gratuitous sex in it and very anti-family attitudes." Rakolta landed on Nightline and the front page of the New York Times. It was, as one Fox executive recalled later, "$100 million worth of promotion" for the still little-known network.

Soon the Bundys will join the Nelsons, the Huxtables and the rest of the great sitcom families in syndication heaven--if they'll let them in. Fox announced today that May 5 will be the final original episode of Married...with Children, at 10 years of age the longest-running entertainment series now on television.

In case you've been watching PBS all these years, Married... centers on Al, a dyspeptic shoe salesman played by Ed O'Neill, his layabout wife Peg (Katey Sagal), their horny kids (played most recently by Christina Applegate and David Faustino), his buddies, the NO MA'AM club (that's National Organization of Men against Amazonian Masterhood), their neighbors, Steve (David Garrison) and Marcy (Amanda Bearse)--and their obsessions with sex, bickering and beer.

The show virtually launched the Fox network. Kicking off the inaugural season in 1987, Married... startled viewers with its raunchiness and helped establish Fox's image as a cheeky upstart.

Then in 1989, a Detroit housewife named Terry Rakolta started a campaign to convince advertisers to boycott the show. "I find it very offensive." she said at the time. "It exploits women, it stereotypes poor people, it has gratuitous sex in it and very anti-family attitudes." Rakolta landed on Nightline and the front page of the New York Times. It was, as one Fox executive recalled later, "$100 million worth of promotion" for the still little-known network.

Married... has drawn low numbers this season (it's the 105th-ranked show, with a 3.6 household rating as of April 13), as Fox yanked it from its traditional Sunday slot to help boost new shows on Saturday night, then returned it to Sunday when that strategy failed.