Why does it take so long?

Depends on the dog, and the breed.

We normally have a 2-3 hour turn around we tell clients. Becuase the dog has to be roughed out , bathed, dried by hand, then finish cage drying, then brushed, then actually groomed. And we do other dogs in betwee dogs are drying, waiting on a bath ect.

Dogs such as say a yorkie, normally only takes about 1-1.5 hours, while a dog like a collie takes atleast 3 due to dry time.

At a place like petsmart they groom sort of like an assembly line. Basically they have one or two people bathe everyone, and while the dog is in a cage drying the person doing the groom is finishing the dog that was bathed before it. The actually groom time may only be an hour but they give extra time because they are doing more than just a couple dogs. Also in case the dog needs breaks or it takes extra time to work with the dog. Especially if it is a puppy it cannot be rushed.
Where I groom I only give about 2 hours, because I work dogs straight through and there is no cage drying, I do it all by hand. It's just a personal thing not to do so many dogs a day and to not have them stay so long. I hope this helps.

I explain this to people all the time at work. It takes so long because of the amount of dogs that need to be done. They get all the dogs started, preshave, bathe etc and then hand dry mostly and then put into a kennel to dry the rest of the way (on some dogs).. Then they start finishing. Usually the first one in is the first one out..

You can always request a time to get your pup out sooner. Especially if it's just a puppy.. You don't want them there too long because of stress, but then it's also a good thing to have them there for a while because it helps reduce separation anxiety and helps get them socialized.

In reality it really shouldn't take that long. I book by appointment and allow 1 hour per dog(most take 45 min.),this way I can clean the shop before the next one arrives. I average 8-10 dogs per day and groom 6 days each week.
The main factor here is time management,97% of the owners wait while I groom and 20% of them actually are tableside while I'm grooming. I guess everyone has their own way of getting it done!