What’s with the high pressure tires?

After airing up the tires for the season on both bikes, they sat about a week. When I came back my back tire was flat, and I saw the tire was prettymuch shot. So at the dedicated bike shop the guy pointed me to a different size that would work on my rims (was 26x1.5 new26x2). But I noticed the pressure on the new one was 40# compared to the 100# of all the others. Is there a reason or advantage to the higher pressure?