With a 3-bet ahead of you ATo is an easy fold. Dont be results oriented and regret a good fold, just because you would have hit and won the hand. Also note that while you would have had decent
equity against their exact
hands, there will also be times, where you are against for instance AK and QQ, and then you are just completely smoked. And this is why, we should generally avoid multiway all-in preflop situations with a hand like ATo.