As someone who has made many interstate trips through Australia's farmland, I can say that over the decades there's definitely been a drop in windshield splatter. It's unsurprising that pesticide deployed at scale reduces bug populations. Even herbicides which aren't intended as insecticides have limited product advantage to being bug-safe (apart from pollinated crops... and even then). Some aren't even human-safe. An extreme example is paraquat, that while being a herbicide, is irreversibly deadly to humans^ when consumed even in tiny amounts.

^ Obligatory Chubbyemu: https://www.youtube.com/watch?v=0VtUGoGZtI8

I would lean towards the urbanization of the land as well. I rarely get bugs on my car in the city, but as soon as I head out to the country at night my car is covered. I had to stop at a gas station back in May not for gas but just to squeegee the windscreen so I could see again.

They have been used much more massively since the 80s, price decreased significantly.

Yes, and advancements have made them both safer and more effective

Are you sure about that?

The McFlies don't think very much