The economics of this are interesting.
Adding 5 minutes to a flight costs the airline about $500. But tight schedules that result in missed connections cost a lot more.
So AA is trying to save money overall by building a bit of slack into the schedule
https://viewfromthewing.com/american-airlines-is-spending-millions-to-add-minutes-to-flights-cutting-misconnects-is-how-it-saves-money/
>slack
Back when Amazon was books only, they always added some slack on estimated delivery. Your book almost always arrived earlier but Amazon realized early on it was better to exceed customer's expectations.