@Prancer - I don't know. I often hear if you can't tip them you shouldn't do ________ (fill in the blank)
Should we tip child care staff, they often make less than some of the examples you listed. As far as I know, they don't get a service tip. Do we tip the medical assistant at the doctor's? They make less than or similar to the Amazon delivery worker.
Should we tip our child's school teachers, lunch room staff, janitorial staff? Should we tip our nurses (as far as I know that's not allowed by employer policies). Should I tip my accountant's administrative staff?