Some providers only take teachers so they can enjoy the same amount of time off. They don't require the teacher to pay for their time off. I quess this is a trade off for the the provider who can afford it.
Providers also want teachers because it is a f/t child which are hard to come by these days so the provider makes certain allowances for this too.
Is it fair or right to the other parents - no. It is the providers choice of course to do this except word gets around to the teachers and then this becomes the providers they look for.
Parents don't really care about our profit margin. Like any business most just want the biggest bang for their buck. I really get your annoyance Alphagetti!