However, my mind developed a similar conjecture to your's: what if the common frequencies of PWM occur within a kinetic visual blindspot of insect vision, like human saccades [0] in the novel Blindsight [1], so that insects are not aware of the LED at all?
0. https://www.ncbi.nlm.nih.gov/books/NBK10991/
1. https://www.rifters.com/real/Blindsight.htm#:~:text=%22There...
They've had many generations to evolve alongside all human false light sources. Insect generations are usually pretty short. Perhaps they just find it evolutionary useful to cluster around human sources of light. Presence of human food, liklihood of bumping into other insects of the same species, warmth, etc.
If human sources of light were interfering somehow, they've had hundreds or thousands of generations to breed out that proclivity.