well, there is not much math there - if your daily commute is on a stretch, which isn't checked regularly, then it is more profitable to just pay the fine.
I live in the center, rarely take anything for more than 4 stops and never buy tickets - if I get to be fined I just pay the fine and go on - it costs me much less than having a card or buying tickets.
I would agree that the fines should be higher and there should be more control, but I don't have the say.