Well a lot of people would think gaining 50 mpg is way better than gaining 5 mpg, since it's 10x as much, but really it just shows that you can't use mpg as a unit to compare like that

More outrageous sounding, switching from a 5 mpg truck to a 10 mpg truck saves more gas than switching from a 50 mpg car to a 100 mpg car

https://youtu.be/oLQmwOX6Xds

Another factor is that people feel more comfortable driving their local roads and get used to usual traffic patterns, which could mean that they're not as alert if something's different.

Eg you're almost home, in your neighborhood, and there's a stop sign that almost never has anyone else there, so you might not look too much just roll through, the one time someone's actually there.