Yor brochure is too basic for so rejected regards.
Your design is outdated, basically you need to know what is the trend now and how to construct a modern, pleasant-looking templates. See what sells on the market currently and what designs are being accepted.
but you know that this is not an issue for sale
Yeah, it is a big issue, because outdated and too basic designs won’t get accepted on the market. You gotta be more creative as the category you chose to apply is quite crowded and only best designs get accepted.