Do TOC do any kind of quality control checks on their RRBs and cease to offer contracts to operators who aren't up to the mark?
Most bus drivers (not coach drivers) only have a detailed knowledge of the routes that they drive on a daily basis, but once they go out of that area, they will have as much knowledge of the area as would an LNER driver would have of the lines going out of Waterloo, i.e. none.
Coach drivers should have a more detailed knowledge of a wider geographic area, but they might not know where the railway stations are and where actual the pick-up points are. For instance, at Hassocks there are two entrances the UP side and the DOWN side, the RRBs are meant to serve the UP side, but an RRB I was on the coach driver missed the turn to the UP side and only went to the DOWN side, so anyone waiting at the correct location wasn't picked up.
Another issue is that, unlike the railways where train drivers cannot just drive a train along any bit of track without having learnt the route, there are not the same restrictions on roads.
You wouldn't get any rail replacement services, if you forced the bus operators to have their drivers route learn the rail replacement routes because there is no time to do it, as bus companies unlike the rail companies do not have enough staff to enable ad hoc route training for RRBs to occur. They do for changes to proper bus routes but not for RRBs.
So, in most cases the driver is just given a photocopied map and told to get on with it.
TfL for its RRBs, puts signage up which helps bus drivers based in East London to be able to drive RRBs in West London (e.g. between Hammersmith and Heathrow with less of a chance of getting lost but it still occurs. That is possible because TfL puts up signage for normal bus diversions, so they have a team who drives around London putting up signs. As TfL is part of the Greater London Authority it has approval to put signs up from the local authorities.
For the TOCs, to put signs up, that would be a minefield and would put the RRB costs up even more.