Could reduce the need for a massive and expensive paint job on change of operator, as happened with the change from Connex to Metro. Hopefully if/when a new operator takes over from Metro, the PT> livery will largely remain.
They've done that with Adelaide Metro buses for many years. Depots run by private contractors (Serco or whoever) on a sticker next to the entrance but the overall livery was the same Adelaide Metro yellow front decal for every bus. I've noticed my local buses - which were once 'Melbourne Bus Link' have been becoming 'PTV delivered by Transdev' so we're obviously headed that way ourselves now.
It makes sense if you are changing operators every few years (as they seem to like doing).