Are you aware of the psychological aspect of how bettors choose between over or under? For starters, over/under bets is a type of sports betting where bettors try to predict whether a combined number of score of both teams is over or under a predetermined value. It is observed that beginners tend to bet on the over side. Why? Because over means excitement.
I think people bet more on over than under, this is understandable because, like you said, over means excitement and shows that the teams delivered on what they are expected to do at optimal capacity. In my mind, whenever I play under, I see it as taking risk because in most of the leagues I bet, it is easier to get over than under. In football for instance, it is very easy to get over 1.5 which will be a winner the moment both teams scores or either of the sides scores two goals. It could vary for other options like corners, cards, and others.
Normally as a new beginner in gambling, it is somehow easy to get a win with over than under, although we all know that luck plays a significant role in gambling. However, just like as the OP mentioned that is the simple truth about it because over is more excitement in such a way that even if you are not yet familiar with other options and teams performances you can easily place a bet on over. Because your own is just for any of the team to score goals, nothing else.