Much the same as you don't hear much about the Tesoro Inca, Royal Sabre, Pantera or other models that are simply ... dated.
I'll admit that I like the current Lobo Super-TRAQ, even though it's been around for a long, long time and only the package color has been changed, and that was more recently. Dave Johnson was hired by Tesoro to work up two models, a gold nugget detector, and a multi-purpose model mainly for nuggets , but with a Discriminate circuitry for other applications to deal with trash.
I liked the original Lobo, mainly because I like more manual control and with it you could adjust the Ground balance for peak performance in BOTH the All Metal and Discriminate modes. Before Dave Johnson got busy on his two units, Tesoro had had a couple of Diablo models. They worked, but didn't work all; that well. The original Lobo was okay, but a little more creativity, I guess, was maybe needed.
A little reflection on some nugget hunting detector history, and I'll be brief, was that most gold chasers were using all of the common production VLF's, VLF/TR-Disc. and some VLF/VLF-Disc. (motion Discriminator) models. Then there were a couple of new entries on the market. Garrett was working on their 15 kHz units, and most other manufacturers were doing similar things, but especially after Dave Johnson made the Fisher Gold Bug. That non-discrimination, All Metal detector worked quite well for hunting the low-conductive nuggets in bad ground. The challenge was on for all of the competition.
Then, good things and bad things happen. Dave Johnson left Fisher, Tesoro hired him to make something to compete with his own Fisher Gold Bug and all the competitors, and he made the Diablo