I think it is indeed partially because fewer people work outdoors (farming, etc.), and even recreational activities like fishing and such seem to be “down”. This despite a growing population.
Plus, we now have much better warnings of thunderstorms, and there are considerable efforts by the NWS regarding lightning safety, such as the “When thunder roars, go indoors” and “Flash? Dash Inside!” slogans.
“I guess the numbers are falling because folks spend less time outside?”
Better weather forcasting and over the past decade installation of warning systems near pools and sports complexes to warn of nearby lightening.