Seems OK at first glance, but if you're in a 65 then the trucks (in the right lane) will want to go 65+. Going 55 in the right lane means they all need to pass you, which causes a domino effect onto the other lanes of traffic. If you're on a 4-lane highway (2 in each direction), going 55 means that trucks that pass you will have to go in the fast lane.

If there aren't a lot of trucks around, then going 55 in the right lane has less of an impact on other drivers. But if there are many trucks (which there usually are, IME), then going 10 MPH under the limit will cause a lot of headaches for all the other drivers around you.

I think you know why: efficiency and safety. Driving fast greatly increases fuel consumption and wear on tires. It makes crashes more likely and more serious.

Why do people need to drive fast? The gains are minimal even if you stay exclusively on a lightly-trafficked freeway. In more realistic scenarios, the gains are almost nothing. You'll just be the first one to the light or traffic jam.

Air resistant. For most vehicles the sweet spot for efficiency is around 45-50 miles an hour. If you go faster than that you start spending more energy fighting wind resistance than going faster

They are not willing to pay the premium, though.

Tell me when highways, bridges, and streets are not paid by gas taxes -- you won't.

Tell me when I can trade money for reliably sequestered CO2 -- you can't.

edit: I didn't downvote them btw