It could be evolution - insects with traits that kept them from cars were selected for. Perhaps changes to the license plates? Changes in the design of cars? Or a general decline of insect population?
[1] https://journals.plos.org/plosone/article?id=10.1371/journal...
Just anecdotally, I see almost no bugs swarming street lights anymore, and have personally experienced the windshield phenomenon on several road trips.
Now they seem to be able to navigate their way out with comparative ease. Open a door or window and waft them in the general direction and they seem to be able to escape.
I've been wondering for a few years if this was evolution.
Still, there is no doubt that the insect population is in a massive decline.
It depends on what the nature of the airflow around a specific car looks like. Bugs have a harder time than air making a "hard corner" but the mass of air stuck at a hard corner can cause other air to go around in a more graceful way and carry the bugs with them.
Coefficient of drag hasn't improved much since the 90s and most of those improvements have been with regard to the vacuum behind the car so aerodynamics is probably only a contributing factor either way.
incorrect
As I've pointed out in another comment, research has shown [0] that counter-intuitively "modern cars actually hit slightly more insects."
It's a reasonable hypothesis, however what this research shows is that we would have expected to see more dead insects on cars had populations remained stable.
0. https://www.theguardian.com/environment/2020/feb/12/car-spla...