Actually, the original Bren Ten sold quite well. Unfortunately for the design, the business managers terrible. They pre-sold guns well in advance of finishing the design and starting production. They did this to raise capital. It is not clear to me if they lacked investors, or didn't solicit investors. In either case, they were then 'in the hole' so to speak, and never could get out. They were always using the most recent sales revenue to pay to produce a gun for a buyer a year earlier.
To make matters worse, under pressure to ship, they shipped guns without magazines, on the promise to deliver magazines later. They also didn't properly QA all guns, and therefore had more warranty work than expected. Once they realized the mess they had created, no investors were willing to get onboard to fix their woes.
They closed the doors with people still waiting for guns, and more still considering purchase.
You have assumed the low sales volume was due to the desirability of the product. It was actually due to lack of production capacity and business acumen.
However, one item to consider is that in the mid '80's there were no CZ syle guns readily available on the US market. Clearly, given the success of the CZ here, the Bren would have sold very well if they had production capacity and good customer service. Today, however, there are not only original CZ's to be had, but also several clones. The Witness clones are even available in 10mm and 45 ACP. Luckily for VLTOR, the Witness guns bear a stigma due to poor customer service reputation by EAA. There are many who like the design, but are unwilling to risk a bad experience.