[Grammar] not least since

[vaibhavmaskar]

Memories linger. The rainy season, which coincided with the genocide in 1994, is hard, not least since skeletal remains still poke out of the ground after downpours. But Rwanda’s terrible history dominates neither public life nor private conversation as it did even a decade ago.

Could anyone explain the meaning of this phrase?

 

[charliedeut]

There are several reasons why the rainy season is hard. One of them, and not the last in the list, is that remains of corpses can still be seen after heavy rain.