Nobody follows the speed limit that closely, in the US at least. If my car was hard-capped at the posted limit I'd have a mile-long line of honking tailgaters behind me in no time
If you hog the left lane, sure. I follow the posted speed limit and it's never a problem for me
You never drive on two-lane rural roads? Getting stuck behind a slow vehicle is torture.
they usually allow passing at specified points
Which are often few, far between, and quite short. If there's any kind of traffic coming the opposite way you can miss your chance over and over again.
Only until speed-limited cars reach a critical mass.