Population growth.
Where I used to be able to cruise straight through (and I ain't THAT old) from A to B is now littered with intersections, stop signs, and stop lights which inevitably are red when approached. Cruise straight through = modest, constant speed in top gear = max fe vs. constant accel/decel, low gears, brakes, etc.
Then the traf**** density sometimes will prevent getting through a red on the first cycle which leads to even more idling and probably more intense jackrabbit starts.
The sheer quantity of firing cylinders at any given moment has forced the development of complicated and expensive computer emission controls (in some cases for the better and in some cases not).
The sheer demand for fuel forces prices higher for all, including those who don't flagrantly burn a lot of it.
The sheer volume and density of motorized vehicles operating, combined with society's acceptance of removal of mufflers, means that one's chances of finding a place where their right to enjoy their own property unspoiled has become increasingly elusive.
Combined with the increased volume of semi-truck traf**** needed to supply the increased amount of consumers with all the plastic disposable stuff they buy then discard a short time later means formerly relatively desolate "country" roads are now filled with trucks, commuters, and mufflerless joy riders. That leads to more waiting for merges, etc.
So, mustering up their best anti-logic, government, churches, and the general population of idiots decide that paying people to reproduce makes the most sense.
"Progress"