TV programs are lures designed to deliver an audience to advertisers.

Situation comedies make up a large chunk of TV programming which attracts huge audiences, millions of viewers, because sit-coms offer escapist entertainment, formula fiction, comfortable characters, and pleasant predictable situations: usually light humor, zany antics, easy-to-solve "problems" which are resolved with satisfying, or heart-warming, endings.

Individual programs are usually geared at smaller segments of the whole TV viewing audience, influenced by the demographic studies analyzing audiences by age, gender, ethnic group, and so on.

Thus, there will be TV shows about large happy families, or single mothers, divorced dads, teen age friends, college friends, singles, golden oldies -- whatever group some producer thinks has a large enough target audience to attract advertisers.

In reality, audience overlaps are common, because of the soft-couch factor: many viewers watch whatever is on TV.