They offer it because very often, the short connection works out. It’s obviously incredibly annoying when it doesn’t, but airports wouldn’t set MCTs to eg 90 mins if they failed 80% of the time.
Single business travellers, people with no checked luggage, those who are familiar with the airport, people sat in first / business or first rows of the economy for whom it takes 5 minutes to disembark… they may all be happy “risking” a 2.5 hour layover.
I’ve never gone through Atlanta but have managed international to domestic connections in just over 1 hour at Newark for example (booked as 3h, flight got moved…). Had good experiences at Charlotte, Philadelphia and JFK too - but I know many who didn’t.
It’s a matter of luck and also of how fast you can run and how confident you are at going through a strange airport without stopping every 5 minutes to make sure you’re on the right path. When you land in the US on a tight layover, you don’t have time to think - you engage automatic mode.
Often, inbound Europe - US flights land up to an hour early (thank you, winds!). However, other times the flight will get delayed because of a technical issue, there will be bad weather over the US coasts resulting in air traffic congestion, and you’ll be sitting in the last row of economy while 5 other international flights are also landing during your same spot and filling up the immigration hall - the perfect storm has gathered for you to miss your connection!
I tend to book risky connections because I always try to fly a day earlier than I’d need to be there. For holidays I wouldn’t mind being delayed a full day - but I also don’t have small children.