Progress as a student is dependant on your practice time. The time spent 'dancing with a teacher' is coaching, possibly, but the teacher can only dance around with you, and not correct important things like frame, footwork, etc - these need to be seen from a distance.
Just dancing around is fun, and sometimes can help, but once you leave the lesson, your 'feeling' of what is happening fades and unless it is reinforced by constant training, it will go away within the week between the lessons.
The 'problem' is that dancing with a good dancer feels so much better than learning with a partner, especially in the beginning stages, which is the first 4 or 5 years. Since the beginner has nothing to compare it to, they think that THEY are dancing better while doing it and because of it. You hear it all the time when a Proam student says either 'they can't do this with anyone other than their teacher' or they can 'really only dance well' with a teacher.
Studios certainly do not want you to NOT improve, but since most folks (most adults anyway) go intoa studio for that positive-reinforced 'fun' lesson that they preclude the harsh realities that accompany real athletic coaching - long hours of practice, obsessive repetition (needed to make the movements 'yours'), and so on. At one hour a week and dancing at the friday social, it'll take forever to improve - the studio can only give you so much; they can't call you and remind you to practice or to think.
in many sports, coaching is not so one-on-one, and of course a world class athlete is still a small percentage of what comes out of a sport, but to blame the studio is akin to blaming the hammer for not making the house look good.
Yes, chain studios do prey on the adult who wants stroking and an instant social life, but the internet today allows for a lot of reasearch to be done, and for people to discuss and interact in ways that were unimaginable until only recently. Use it!