There is no evidence for that. There is no dry tailgating culture. You try to equate going out to eat and having a beer or wine with your meal as the same as people tailgating so they have a few beers as well. People who watch the game at home also have a few beers and can bbq and can play games. They can do all of those things with their friends, and then they could go to the game after if there was a DD. That isn't the culture, however. Also, they don't go to the tailgate to stay sober. The casual beer at dinner is not the same amount of alcohol consumption at a tailgate.

I put forth that tailgating became what it is only because drinking before the game was a thing. Many stadiums didn't allow alcohol in the stadium, so people drank outside. It is the same reason people drink before to the bar, so they don't have to pay the higher prices there. Enough people drank outside that they weren't all rounded up and thrown in jail as public intoxication is illegal. It then grew into a big party tradition before the game. It is a fun tradition, even for non-drinkers. The party started because of booze as most parties do.

If you have ever been to a Mormon party, they are so bizarre compared to the rest of the world. Parties happen because it is an excuse to drink which is a social lubricant. They don't naturally occur without alcohol. I just texted a few random friends that have nothing to do with BYU, Mormons, etc. I asked if drinking wasn't at tailgating, would any of them go. The answer was, what is the point? I then asked if they would go to a great BBQ joint if it didn't sell alcohol. The answer was that they would if the BBQ was good. They go to tailgates as an excuse to drink. They do go out to eat for good food. Games at the tailgates don't take away from the booze and beer at dinner doesn't take away from a good burger, but each has their specific reason for existing.