A long time ago people who worked in gyms tended to be those who worked out. It was rare to have someone with a degree (it was rare to have many degree programs outside of the world of sports and coaching). Group exercise and personal training certifications grew out of a drive for the industry to position itself as more of a profession, to create a way to help those with a certain level of knowledge stand out, and to set some standards as to what that knowledge should be. As the profession grew, as more jobs were available, and as more people got certified more people began also to enter the profession by way of getting a degree. One could imagine that things could have gone differently and fitness could have been offered by hospitals first, rather than by private gyms, and there could have been a standard where all trainers would be expected to have credentials more similar to an exercise physiologist.
But in the world we have there is a system that has grown up that most gyms look for a well known national certification. That credential does not say one has the deep and thorough theoretical knowledge, but has the practical knowledge, and as was already pointed out, will continue to get new training at regular intervals. A doctor goes to medical school, but as part of their licensure must take continuing education… the same with a lot of such professions.
I see from your profile that you have a degree in a fitness field. It sounds like you have found some places have wanted more. The good side to this is that given the knowledge you have you would likely not need to spend a lot of money on training, but could buy a study guide and relatively quickly get your national certification (certainly more quickly than the other person with just the certificate).
I think Harris is right. Places that are hiring usually are looking for more than just one thing. (and frankly every part of fitness has so many people looking for work it is very much a ‘buyer’s market’): A national certification is a baseline that you know what you are doing and reduces liability to the club, insurance shows professionalism and also reduces liability, a degree on top of that shows commitment and I suspect allows for more upward movement for some jobs, and experience is extremely desirable as it decreases the amount of time the company has to spend on training.
This is a very interesting question and has spurred some really well thought out responses. Thank you for posting it.