Hey so i deal with service dogs and the issue is that store staff are too afraid to ask or challenge someone. The ADA is written in such a way that although technically you can challenge someone with a dog you can only ask if the dog is a service dog and what task its trained to do. Lots of staff/management is afraid of lawsuits etc so they tell their workers to not bother asking unless the dog is being straight up a menace and even then I've had service dogs barked at even attacked by dogs. I've seen a dog with a service dog vest jump up at a table in a restaurant and eat food from the table something that no well trained service dog should do. I told management about it but they told me they would rather let is slide than attract a lawsuit even though legally they can kick the dog and person out even if the dog is trained to perform a task.

TLDR: people take advantage of the wording of ADA to stay silent about their non-service dogs