100th place being 2:39 is in line with typical NY marathon results in recent years, and that's more indicative of the current state of distance running than it is of a post-pandemic year with multiple major races crowded into a brief time frame.
Outside the sharp end of the race there's long been a precipitous fall-of in times, which has been a trend in road racing (marathons and other distances as well) for years now, and it's been discussed on these boards. NY -and other majors- do get massive numbers of entrants, but the number of runners who actually race -you know, push themselves to the limit and leave it all out on the course- has been dwindling for decades. The vast majority of entrants treat whatever race they're in as a street fair rather than a competition.
Here's what the 100th place time was at the NY Marathon for the last five pre-pandemic editions, along with the year 2000:
2019- 2:33:53
2018- 2:35:08
2017- 2:37:15
2016- 2:39:28
2015- 2:40:07
2000- 2:37:11
But if you go back almost 40 years to 1982, long before supershoes and when the race had far fewer entrants, 100th place was 2:25:45