Remember that Cop26 is being hosted and funded by Westminster. Holyrood could argue that if they had a completely independent budget they could sort it.
Abellio and Holyrood have done a poor job of presenting their case.
As lockdown eased there was a shortage of both drivers and RMT grades. That's why they were offered a major enhancement to work rest days. New drivers take at least a year to train and so there is still a shortage and the enhancement continues but will, AIUI, be reviewed every three months. RMT grades take only a few weeks, there was no shortage of suitable candidates, and according to Abellio, and presumably the Scottish government, there is now no need to pay this bonus. They would rather spend the Transport budget on essential railway services.