Why don't aircraft weigh themselves?

[ppppilot]

Good paper that. I remember when working for a cargo airline, Metro II, Metro III and Merlin IV. Dozens of times when I arrived to the plane the nose wheel was almost in the air and when I asked to the ramp agent, he always was sure the airplane was perfectly loaded. Reading the article, I can see that the heavy opposition comes from cargo operators. Another curiosity is that FAA requires a 1% of accuracy to the system. Therefore. FAA is assuming that only a 1% of error could be found on 100% of flights or that only a 1% of the flights do not comply with the loadsheet?… Boy, we don’t live in the same world. Probably all of us have seen those small tractors to pushback the bus, remote control commanded that only lifts the right or left main gear. It could be a good weighting device by only applying measure units to the strength needed to lift the wheel. Sequentially the 3 wheels, of course. If such a cheap thing or the nitrogen pressure of the wheels, could be used to random control of the airplanes and FAA only finds a 5% of error then I fly for free the rest of my life. Is it not the same difficult to weight the fuel on board? That weight could be used to check the onboard weight system. Ok I know I am going too far. Only trying to give some thoughts just in case someone of the FAA or the CAA read my post.