If your dogs don't need teeth cleaning, yay for you! But don't assume that extends to everyone else.
9 out of 10 dogs that come in my shop for grooming have disgusting mouths and they DO need it. Most of the older ones have teeth literally rotting out of their heads, untreated abcesses and breath that could kill you. It is very unusual to have a dog older than 5 come in that doesn't have very severe dental issues. A large part of this I think is that I work in a low income area and deal with some cultural differences regarding care of animals. Thin dogs, untreated injuries, etc are also very common.
I try and educate, but people laugh off routine care (brush his teeth! Hahaha! Grandpa didn't do that! It's just a dog!) and when the lack of dental care finally becomes painfully (literally) obvious they complain that it's too expensive to fix, so the dog just has to live in pain.
It gets very frustrating.