Actually if you look at the numbers on the unofficial spreadsheet, most of the reservations were for the tri and duel and very few were for the single motor.I recall Mr. Musk expressing his view on the single motor truck as being less than his desired ideal truck product after the debut. The CT is a conglomeration of a lot of truck configurations and while it can not be everything ( long bed and short wheel base ) his passion was that it be a BA truck, not an El Camino.
Pick up trucks, empty, can spin out at every intersection without any effort, especially on wet painted surfaces. The single motor variant would be susceptible to this handicap and does not make for a BA truck. After the debut, he seemed to realize that the truck needed to be AWD as a minimum, anything less than would be puny.
I too believe, he does not want to produce the single motor variant but realizes it was the product that caught everyones attention at 39,9 and he does not want to be accused of misleading marketing practices.