I know nothing about it but I have seen hints and suggestions over the years in the news media. The problem is that the news media get around by car and so are not very interested in public transit.
Without any information, I am free to indulge my imagination. The problem is that hideous, irresponsible document called the Bill of Rights, which guarantees that no one is deprived of property without due process. So suppose a Muni worker decides to go to the ball game. He is listed as a no-show; Muni decides to dock his pay. He protests, saying that the Bill of Rights entitles him to a hearing before his pay can be docked. Muni's problem is that the cost of the hearing -- a hearing room, a hearing officer, relevant employees taking time off to attend -- is greater than the cost of the no-show, and this is assuming that the employee doesn't feign illness in order to run the cost even higher. So a bargain was struck: As long as you don't have more than 13 (or whatever the number might be) no-shows in a year, we won't dock you.
Now, if it were up to me, I would spend whatever it took to hound these lazy SOBs to the ends of the earth. Just goes to show how unsuitable I am for public employment.