Why do T.v. themes change throughout the years?

My history class is doing a project, and i need to know WHY television themes changed from the 80's into the 90's.

I have searched so hard for a reason and im drawing a blank. In the 90's there were a lot of family oriented sitcoms whereas the 80's were a lot of comedies and some sci-fi's

a lot of the major events of the 90's were acts of terrorism and im trying to find a way to relate how

terrorism changed the themes of television.



the only ideas that ive yet to come up with is:

- that people were trying to get their minds off of the terrorism and so they produced calming family oriented sitcoms

-the 1990s was a decade of less war (except the beginning the the 1990's having the gulf war) and it had been a while since there hadn't been war and so they formed shows that reflected the peace



and

-people were worried about the end of the 90's and in turn the end of the world with Y2K and so they decided to focus on family to ease peoples minds



all of these ideas dont have solid proof and so if anyone can help me at all, it would be greatly appreciated.

Thank you in advance



(all of my information is about the United states. any wars that were going on didnt really involve the united states and as far as television goes, im only concerned about americas tv. )Why do T.v. themes change throughout the years?
the changing of the themes may be due to the fact of the occurrences around them

hope i get thumbs