Because the types of failures that people experienced line up directly with design choices made in order to fit the pen form factor: overheating, heater failures, battery failures.
When you try to force your design to conform to a certain form factor, you have to make compromises. In this case they were forced to use proprietary batteries, a heater that was very small, with difficult to clean channels, and easy to break when cleaning with iso.
Compare it to a standard stem style vape that uses an 18650, like a TM, Milaana, Toad, etc. You can have more room for designing a heater that doesn't overheat or clog easily. You can insulate the battery from the heater. You can use a variety of 18650 batteries from reputable manufacturers. You can keep the cleaning to inside the stem, so that you don't need to clean the heater, putting it at risk.
They could have done all this and kept it to a very sleek and stylish design. Something like a Toad but smaller, metal, and mass produced.
I also always found it funny how the pen shaped design made for a very short vapor path, which forced many who are sensitive to hot vapor to use water pieces. It seemed so silly to take a product designed to be small and pocketable, and use it with a water pipe, negating the benefits of that form factor.