I wonder what percentage is pesticides vs development? I currently live in an area(US) where a drive to the nearest city of size absolutely coats my car in bugs. US, mostly farmland(soybeans/corn). I wasn't here 30 years ago so can't say there's as many as then, likely not. But if it were only pesticides I'd expect the rural areas to have less bugs than the more developed areas...
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.
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