I think fans saw a lot of losing and decided to spend their time and attention elsewhere. If we had been a winning program the fan decline would have been minimal or non-existent. So called "casual" fans see a winning team and they stay for the fun. Give them a losing team and the party ends. I doubt the casual fan cares who we beat, as long as we are winning. Look at the difference in tone and attention around the football program this season. Our schedule was much better than a typical AAC schedule. The difference is winning and being competitive.
There are teams in Power 5 conferences playing all the teams we care about and they can't draw flies because they don't win. "Winning cures all" is a saying for a reason. The American was4 heaven or really ideal, but had we been going 8-5 instead of 3-9, I think it would have been different. But none of that matters now.
As for study before the move, the first plan was to stay in the AAC for football and move Basketball. I just think it is hard to compare the conference change impact when we were losing so much. Things look great now and that is what matters. I just balk at the AAC was the reason for everything belief.