Me thinks your logic is a wee bit warped there NZKiwi, an almost angelic name to boot, I might add.
Duty travel tech crew are booked firm, no travelling public displaced!
Another thing ,no tech crew , no go , which is the only reason tech crew would displace paying passengers otherwise Alan and every other passenger would miss their party.
Plus it's contractually agreed upon, for techies to be up the pointy end vieing against all the management wunderkinds and fatigue issues might have something to do with the whole enchilada for tech crew as well.