Speed limits + cars set an implicit speed minimum that is required for both safety and to not cause mad cars who are trying to go the speed limit. There's a reason you'll get pulled over for going 20mph on a US highway, and it's a legal oversight to have high speed streets that don't have minimums, or worse are designed to share with bikes even though the average bike won't hit a safe speed minimum.
The whole point of the thread is that bikes and cars sharing the road with these sharrows is dysfunctional so yes, that's the point...
> The maximum is there precisely so drivers can respond to slower traffic, not so all traffic will conform to that maximum.
I don't know of a single place in the US where the maximum isn't treated as something to conform to. I've driven in the Northeast, South, and California. You'll get honked at for going noticeably under the maximum in all three places. What you describe just simply isn't the practicality of the US roads.
I absolutely understand what the speed limit is. And understand that in most jurisdictions it is perfectly legal to go under the speed limit, however that makes it no less annoying. When you are following someone in a car going incredibly slow are you not annoyed? You want to pass them, but you don't want to do so unsafely, so you have to wait for a safe opportunity the whole time just wishing they would go the posted speed limit. Then someone behind you gets even more impatient and passes both of you creating an unsafe environment for everyone.
In many jurisdictions there is also a legal minimum speed stated within the statutes, often based on some value below the posted limit. They are often unknown to most drivers (and cyclists) because the minimum speeds are almost always not placed on signage on the roadway. But legally, there is often a minimum speed as well as the more well known and visible maximum speed.