This is the most econ-brained response possible. Why would the success of a public policy be exclusively defined by revenue generated?
If you want congestion to go down, keep raising the price. It will eventually go down and revenue could go up a lot.
Politics is tricky, don't take so much you make people affected mad enough to undo what you wanted.
It’s also nyc primarily in charge of it and nyc constituents probably are in favor of less congestion and more money.