Changes are stymied by bureaucracy put in place due to fear of litigation. The primary reason that things are studied, studied again, given community input, and checked for environmental impact is that if a city or municipality gets sued due to a road change, the onus is on them to demonstrate that they didn't create an unsafe condition. For example in cases where cars crash and are liable for property damage, car owners try to sue the city to claim that the area was unsafe. Pointing to a massive paper trail like this removes liability from a set of city or municipal concerns.
Nah, that's just the bullshit they tell you.
A municipal or state government will not be held liable for the consequences of shitty infrastructure unless there's like 9/11 levels of "the system was blinking red and you ignored it" and even then it's coin toss at best. Like maybe if they kill a ton of people there might be a lawsuit that sticks that's sooooo unlikely for the scope of the kind of thing we're talking about here.
The bureaucracy is put in place because none of the people putting it in place are paying for it, headcount is power, control over resources is power, etc, etc, and all the other perverse incentives you see in government workplaces. And of course once the gravy train is running all these parties have an incentive to keep it running.