Roads tend to have a speed where people feel comfortable. In theory, road engineers design roadways to match the desired speed. In practice, that doesn’t always happen. Even worse, cities/towns have been known to lower the speed limit to drive revenue.
Usually, when people talk about the topic, they’re trying to calm local traffic. But the concept applies to highways where speed limits can be pretty arbitrary. Plenty of interstate where 80+mph feels safe, but is posted at 55 or 65.