There seems to be an inordinate number of no-hitters at the ends of baseball seasons.
There are. Indeed, the most popular single day for no-hitters is the last day of the season.
The most popular months are September, followed by April.
And, as you might suspect, there is a reason. April and September are the coolest months of the season. And air temperature (actually, air density) importantly affects the incidence of offense in baseball. The cooler (denser) the air, the less distance a batted ball will travel. And the more a breaking ball will move.
An amplifying factor with respect to the last day(s) of the season is that, often, one team is not only playing for nothing (and, thus, intent on getting it over with and going home), but they might also be playing a lineup full of scrubs.
In other words, the high incidence of no-hitters this time of year is a perfectly natural phenomenon.