Thing is, Aerodynamics, better wipers / washers etc is one reason the other could be the number of vehicles.
What do you reckon, 20 times more vehicles on the road today compared to the 70's? More vehicles, less insects per vehicle.
Regular car washing too, get your car washed anywhere and many do every week.
Think it depends on where you live too, we're semi rural and there's been no shortage of insects, Wasps in particular.
Personal favourite 2 insects are the Lace Wing and Shield Bug, never kill 'em :-)