Why can't hydraulic bicycles be popularized?

The hydraulic transmission is unstable. Can the hydraulic pressure be controlled? Cycling is fast for a while and slow for a while. Who can stand it? It is easy to decompose and has high pollution requirements. Do you think you can guarantee that there are no impurities? Bicycles are everywhere, too oily to be repaired. Not everyone can fix it. Who has spare valves and coil oil at home every day? Is it easy to buy hydraulic oil? However, this is a good new invention. If we continue to develop, it is possible, for example, to use servo valve proportional valve, and then open a hydraulic oil gas station in the street. Haha, good, waiting for your efforts.