I nearly always tip 20-25%, never less than 15%, and my stylist is one of the owners of the salon. Gratuities for services like this were common long before minimum wage was ever heard
of - that is not
where it came from for food servers, etc.
That said, tipping anywhere other than restaurants and hotels hasn't always been practiced in small towns and rural areas the way it has been in New York and other urban areas. Some who don't do it may just not have caught up with the times yet - they may just not even think
of it. I was guilty of that myself at the dog groomers when I first started using one 10-15 years ago.