I tend to rant about this topic pretty often, but I'll keep it short. Basically, in the early days of television there wasn't much choice (only a couple channels) so the government put someone in charge of regulating what should be allowed on the air. The man that they chose was very puritanical. To give you some idea of how puritanical, just look at shows like "Mary Kay and Johnny" and "I Love Lucy" which broke barriers which now seem ridiculous and idiotic. One barrier that they broke was having a married couple sharing a bed. Yup, you read that right, up until that point, married couples were shown sleeping in separate beds because if they shared a bed, then that meant that they had sex, and that kind of smut wasn't suitable for television.
Another barrier that they broke was having a pregnant Lucy on the show. The executives were extremely uncomfortable having a pregnant woman on the air and finally allowed it after Lucy and Desi consulted priests and rabbis who said they didn't find it morally objectionable. Despite this, they were never allowed to say she was "pregnant," only that she was "expecting."
They've slowly lightened up and allowed more realistic content, but despite all of the advances over the years, the rules are still very uptight.