Transit should be outrageously expensive to add. (see the recent subway expansion in New York and in San Francisco) It should be outrageously expensive to operate.
Transit should shut down often for floods, strikes, the "wrong type of snow", "leaves on the tracks", crowds of people (good job San Francisco, LOL), maintenance, terrorist attacks, and many other random reasons.
Transit should increase crime.
Transit should go to the wrong places. You ask for it to be installed where it is needed, but instead it ends up a mile away because that was where it is possible to build.