It doesn’t work in high traffic areas, because the tap areas become impossible to get to if people actually use them - same bottle neck problem. On busses they

It doesn’t work in high traffic areas, because the tap areas become impossible to get to if people actually use them - same bottle neck problem. On busses they are de-facto soft gates, assuming the bus driver yells at you if you don’t use it - which often they do. And why would they give up that sweet sweet rush hour revenue?