I'd suspect it's more to do with the onboard CCTV and Driver monitoring
equipment,which being visual only,will not pick up the Drivers "advice" to
passengers.

Drivers actually picked up on CCTV opening the doors at anything other than
a fully secured and pre-vetted location would most likely,a month later, be
required to approach Sir Brian Souter or Tim O Toole on bended knee,whilst
pleading for their lives.....

Public Transport now has forgotten all about the likes of Bus Conductors
advising their passengers to "Hold the Bar now please Ladies...Ding Ding"