Because people passing you is very slightly more dangerous than people following you. It’s not a big deal most of the time, but when everyone passes you across thousands of hours it adds up to a significant risk.
Why would anyone want to pass you when you’re moving at the speed limit? You are at the speed limit and everyone passing you would be beyond the speed limit.
I honestly can't tell if you're trolling or not. They would want to pass you because human drivers aren't rigidly law abiding machines. Is there a large portion of people that go exactly the speed limit, or even lower? Sure. Is there also a large portion of people that speed virtually every moment they're behind the wheel? Yes, absolutely. And I wouldn't be surprised if that were the larger population in most areas. No one who actually drives with any regularity would ever be surprised that people are speeding to pass them.
