Posted speed limits are there for a reason. NFB is 35/45 because of all the traffic that has to pull in / out of complexs/houses/malls.
Speed limits are also based on visibility. The further you can see, the higher the speed limit is probably going to be.
Traffic patterns, visibility, residential/commercial zoning, all have stuff to do with speed limits. Not so much your “they want your money theory.” It’s more of a “More than half the population is made up of fucktards that can think with common sense.”