I didn't want to have to do this but, YES TRUCK DRIVERS CONTRIBUTE A LOT TO AIR POLLUTION.
In terms of companies or industries: they employ tons of trucks which haul lots of stuff up and down highways all day and night...which contribute significantly to smog, and the release of chemicals into the air (which can cause nose bleeds, headaches, skin irritation, and other ailments). I got a nasty taste of this first hand when I ended up on the highway with my bike and the exhaust fumes triggered an asthma attack. Small towns where industries begin mining or some other shit requiring 100s of trucks to traffic the area daily, suddenly become dens of air pollution with big-city levels of smog.
If you are looking at an industry and say "ok, you are basically polluting way too much, you need to reduce your emissions", then one way industry can significantly reduce their emissions is to make sure the trucks which they employ are not exceeding certain limits.
Yeah maybe the singular truck driver is too moronic to realise WHY he has to watch his emissions, but it doesn't change the fact that it is necessary. They aren't singling out people, they are singling out INDUSTRIES and COMPANIES which happen to employ people.
These truck drivers are dumbasses.