Think the end of the article pretty much nails it.

Tesla needed to install and remove it at a service center. Owners couldn’t remove them themselves. I think it was pretty much dead on arrival at $16,000.

But I think it could also be as simple as it’s not worth producing due to demand – both due to insufficient people reserving it and not enough Cybertruck buyers to create a market for the range extender.

Therefore, the range extender is dead for the same reason that the Cybertruck RWD now has the same battery pack as the AWD instead of a smaller pack for less money: the Cybertruck is a commercial flop, and it’s not a high-volume program enough to justify making several battery pack sizes, including a removable one.