Had there been any saving in running the Hiace on petrol, then you won't see scarce public transport on CNG off days. Those drivers and conductors definitely won't like to sit home in vain, knowing that they have to be on road every day to make both ends meet.
It was poor govt. policies from previous govt's that allowed the installation of CNG in public transport unchecked. Those transport guys are culprit to some extent, but not to 100% extent.
You see huge saving in CNG and invest 50K. Those guys saw savings and invested 200K (Engine swap + CNG + 2-3 cylinders), in anticipation of brake even in some time and then be profitable.
P.S: Mass transport system is the answer to all these problems, and implemented all over the world. Pakistan is probably the only country where Railway system has been deliberately destroyed, then the bus services like Varan were never allowed to succeed. And the end result is the hiace mafia.