There are a variety of reasons why your product would have been turned down.
We suggest that you start by looking at your product promo images. Your promo images are the #1 thing customers judge your product by, and therefore are the #1 thing that DAZ judges your product by.
Compare your images to some of the best selling products on DAZ. Are your renders as nice and compelling? Do you use dynamic lighting? Does your product look like someone could reach out and touch it?
The best products and promos often require long render times and hours of work to achieve just the right look. A customer is not as interested in your back story, how hard you tried or how many years you have or have not trained. They are interested in what looks cool and will look the best in their renders. As the product's creator, YOU should be the best authority on how cool your set can look. You Promos much show this.
Some other reasons DAZ may have passed on your set:
It was for an older character that is not as popular with customers.
It is for a niche that is already crowded, such as poses, add-on texture sets or character morphs.
It was too close to an existing product or ip.
It just didn't appeal to us.
We try to be encouraging and help all artists improve their work and move forward. Unfortunately we cannot always provide detailed feedback on everything we see.