After reviewing the ads from Super Bowl '85, it struck me how subdued they were, compared to a random sample of '80s commercials. It's as though they were trying to not take you out of the game itself. Today the relationship between ad and program has become inverted: everybody is on the edge of their seat for the commercials, and annoyance sets in when that stupid game interrupts them yet again.
When did this shift in focus occur? Here is a graph showing how common the phrase "Super Bowl ads" has been across time among the books in Google's digitized library. The graph looks the same when similar phrases are used ("commercials" or "advertisements" instead of "ads", and "ads / etc. during the Super Bowl" instead of "Super Bowl ads"). "Super Bowl ads" is the most common way that the topic shows up, though.
They start attracting attention in the early-to-mid-'90s and have taken off since then. I searched the New York Times for these phrases to see what they were saying about them. The occasional mention that they received pre-'90s was to emphasize how expensive they were, not that they were an entertainment draw in themselves. Only in the '90s and after did they start talking about their content.
In an earlier post on Super Bowl national anthem performances, I reviewed how they changed from normal to exaggerated. The turning point seems to have been 1991, when Whitney Houston pre-recorded an over-the-top rendition, and it only got more diva-like after that. By now there is so much warbling around the melodic line ("melisma"), or such a slow, drawn-out tempo (it should take a little over a minute, not two and a half), that the song gets lost. Because it has become a showcase of uniqueness, the players and the audience in the stadium and at home cannot possibly sing along. It is no longer sung to bind the listeners together and get them pumped up, but to serve as an entertainment spectacle in itself.
Finally, there is the halftime show. In the good old days, the performers were not current stars (or even old stars, most of the time), and they were not there to promote themselves. Rather, it was usually a marching band, in keeping with football tradition. And there was an over-arching theme that celebrated something outside of and larger than the performers -- a salute to the Big Band era, Mardi Gras, etc.
Looking over the list of Super Bowl halftime shows, there are two shifts away from tradition. The first is the replacement of marching bands, or the odd oldies star, by current mega-sellers. That began in 1991, when New Kids on the Block took center stage. Then there was the removal of larger themes from the set list, and making it all about the performers themselves, which began in 2005.
Here's a graph showing how common the phrase "Super Bowl halftime" has been (adding "show" gives the same result):
There are isolated years where it was talked about in the earlier history, but it's not until 1989 that it receives regular discussion.
Putting all of these changes together, it looks like the early-mid-'90s saw the decisive break away from the Super Bowl as national sports ritual to the Super Bowl as insipid pop culture overload. No wonder the last one I remember was Super Bowl '90 (after that the names of the star players are only vaguely familiar). It became impossible to stay locked in to the game itself, and I'm not enough of a football fan to suffer through all the junk just to see who wins.
This is worth keeping in mind when you hear about viewership records -- those viewers are not talking about the game the day after, but girls talking about how fierce Beyonce looked, and guys talking about which commercials were dumber than which others.