They are highly custom shoes for highly competitive athletes and for them to meet regulations they need to be sold (or available at least, as I understand) to the public. Marketing such items, that probably have a very limited usable lifespan, as well as being fairly custom fit, wouldn't make sense to market and sell to the general public. Nike make their real money through said athletes winning major events and the additional value it then adds to their overall brand.

As an aside, the most expensive Nike's sold are the ones they make the least of.