I think that fining bus companies is not only a silly thing to do, but also detrimental to commuters' interest. The bus companies will simply write the fines to costs in their ledgers. If costs are too high, they show the ledgers to the PTC and apply for fare hike, and the commuters end up paying for the fines away through higher fares.
I think that individual executives found responsible should be fined, not the company.