Funnily enough they never seem to pick the days when there are delays.
Oh and the BTP being present is overkill and should be paid for overtime by the TOC's the BTP are not beholden to the TOC's.
Delays could well stop RPIs making the train to work on, having been delayed themselves (how do you think they get around?!). They have shifts to do, so I doubt they turn up for work and think 'delays? let's go for a cup of tea' as they have to log the routes they do - and someone will soon ask why they didn't do anything for hours on end.
However, when there's major disruption then RPIs are often expected to down tools, so-to-speak, and start performing basic customer service duties and other things to help passengers (instead of seeking to prosecute them!!).
As for BTP, why shouldn't they attend for stings - along with local police when doing blocks at stations? Given the connection to ticketless travel and crime, I am surprised they don't do it more often (given how successful these operations are). The police can and will do additional checks on people and regularly find people that are wanted, carrying drugs and so on. BTP aren't just the slaves of the TOC - they get results too.