Earlier quoted context omitted.
Personally I feel it's fine for them to operate at a loss, it's a public service, akin to the fire department or library. The amount of good it does society to get cars off the road is staggering. The lack of bus drivers simply comes down to an unwillingness to pay more. It's the exact same problem with teachers, where the wage is extremely low but they would rather just have a shortage rather than paying more.
Crucially, the road network also operates at a loss
It may help to either tax them directly, or indirectly via diesel. Yes, costs pass to consumers, but it would also encourage more done via ship and train, I feel. Even that would be a huge help to clearing up traffic and lowering infra spend.