Well…, for all your folks who like it because your parents were teens back in the 70’s:
I say: "buzz off!!! The show wasn’t meant for you!

The original target audience was those of us who actually were teens back in the 70’s.
No–you are wrong…The date is important.
That’s why they named it “That 70’s show”.(The network could have called it something more general, like “Happy Days in high school” or “The Eric and Donna show”, for example)
I think the name was a deliberate attempt to attract an older audience—people who would find it not only funny, but also nostalgic, because they had actually been there in the 70’s.
Do I have a cite? well,…no!
But I do have a bit of evidence --they used a unique plot device.
In every episode of the first season, there was a little break and a cut to a piece of nostalgia.For about 2 minutes ,the screen would fade to black-and-white* and the actors would re-enact a scene that would be very familiar to anybody who had lived through the 1970’s.
The scene might be a re-enactment of a popular show of the 70’s, including the now-forgotten theme music. Or, even funnier, the scene might be a re-enactment of a typical “Educational movie” of the type that a high school student would have been forced to watch in the 70’s.
They only did this, I think, for the first season. Afterwards, they dropped it. My guess is that they watched the ratings and checked the demographics—and found that the audience was younger than what they had expected.So they started writing more for today’s teens, and not their parents–and then the show became just another sit-com.
*(Remember,back in the 70’s, people were used to watching in black and white. Many people had color, but half the programs being broadcast (movies, old re-runs,etc) were in black and white