Hi.
As I haven't been a tech for anyone or having had a tech myself, this is sheer speculation.
Techs don't get paid extremely well and therefore they have to work when they can. That means that they can't adjust their working schedule according to the tumbleweeds, eh musicians, when they are on their insprational stage or what ever

.
Also the techs are pros, so a pro is a pro no matter what the work. They're all good, some exellent and even the last one in the phone book will get the job done, well.
When the next tour hits, one of them is bound to be available, and that's not necessarily the same as the one year before.
Like said, sheer speculation, someone more knowlegeable about the subject will chime in I'm sure.
Regards
Sam