Hard to say why, maybe it doesn't suit the user's needs or lives up to one's expectations. I can honestly say that mine has been sent back to Minelab for a few small problems and was promptly fixed. I've had mine for nearly two years already and recently my battery compartment leaked while it was submerged under salt water. I promptly called Minelab and shipped them my ctx, in less than two weeks later I received a new control box and battery. They do a great job with answering your questions and addressing the issue promptly.
I have found so much with my ctx, more than all other previous machines I have owned combined. I love the weight, feel, and performance. At times I have thought about trading it in for an ATX but I think I'll stick with my ctx for now. I will tell you this...if you properly maintain this machine by not throwing it around and keeping it clean, rinse it off with fresh water from your beach excursions then it should last you for many years.