They are probably trying to sell as many "First Edition" cars as they can. These probably represent better margins on a per-unit basis than the base model with minimum options. For certain they are better in terms of revenue. Once FE sales start to slow down, then they will likely open ordering for the base cars.
Delaying base availability also allows more time for people to become accustomed to higher prices. Based on my and other people's guesses, the base model for the US will likely be not that much less than the FE 1.0 prices. My guess would be $89,999. The more time Lotus allows to pass between the delivery of FE 1.0 cars and the availability of base cars, the fewer customer complaints they have to deal with.