That's a nice strawman you're creating there. In some airspace classes and flight regimes an aircraft has more variables, especially when you account for possible failures. If an aircraft has a mechanical failure it can't just pull over and stop.
There are about 46000 aircraft registered in the USA, plus more that sometimes fly in from foreign countries. Many aircraft were manufactured decades ago by companies that no longer exist so major upgrades aren't economically practical.
There are about 46000 aircraft registered in the USA, plus more that sometimes fly in from foreign countries. Many aircraft were manufactured decades ago by companies that no longer exist so major upgrades aren't economically practical.