The i8 is to BMW what the Model T was to Tesla, it was something to gain customer attention and it worked very well. Having been sold for so many years and still going, there must be a demand and those who can't afford the i8 will have other BMW options.
If you meant Model S, then you're wrong. The original tesla roadster was more like BMW's i8 to show that EV's don't have to be boring. Closest thing BMW has to a Model S is the i3, but even that's not worthy of the comparison.