I used to think like that when I was young. Then I learned I was short-sighted, and that every time there are traffic rules (including speeding) they (almost) always make sense. Sometimes they don't, true. If you then have contacts within the (local) government they love to get proper feedback from citizens.

To give an example: there's a school nearby where the sign says 30 km/hour. It is an important road people who live in my neighbourhood, connecting them to their home (commute, shopping, etc). I drive on my bicycle crossing that road. Do I assume people drive 30 km/hour or 50 km/hour? Cause many people drive 50 km/hour there. When kids go to/from school people might drive 30 km/hour, I don't know exactly how that works. Many might not even know there's a school there. Even though the sign says there is, perhaps that gives the mental note: "..but it is Saturday." If we're going to arbitrarily ignore traffic rules whenever we see fit, it is going to lead to chaos.