Because of a court ruling so called “fleeting instances” of indecency or profanity are allowed on broadcast television. CtizenLink reports that federal legislation to close this broadcast indecency loophole is stalled in the U.S. Senate. Excerpt:
Legislation stuck in the U.S. Senate would give the government more power to clean up television.
In order to ensure the Federal Communications Commission’s (FCC) ability to fine broadcasters over "fleeting" instances of profanity or nudity, the Protecting Children from Indecent Programming Act (S. 1780) needs to be voted on by the full Senate.
…
Weiss said the law is needed after four television networks sued the FCC for the right to air profanity at any time of day. The 2nd Circuit Court of Appeals ruled in favor of the networks last year; the FCC has appealed the case to the U.S. Supreme Court.
“The networks act as if they own the airwaves and are fighting with everything they have for the ‘right’ to pollute them as they see fit,” Weiss said. “The law, however, states that the public owns the airwaves and has some say over how they are used. We have an opportunity right now to directly impact our culture, but we must make our voices heard for that to happen.”

Graphic source: CitizenLink
NOTE: For different conservative perspective on TV indecency regulations check out Stuart Epperson’s testimony before the Senate Commerce Committee in 2006 which was reposted at Townhall recently under the title “The Law of Unintended Consequences: Well meaning efforts to target indecency could come back to haunt us.” Conservatives often disagree about the proper role of government in these matters, but many conservatives recognize a legitimate role for government to prohibit indecency on publicly owned wavelengths (much as governments rightfully prohibit public indecent exposure).