I don't think the accelerators/funds are missing the obvious, but I do believe that (because of the high signal-to-noise ratio of the startup bubble) many rookie founders don't discern the importance of this process to their success, and end up "hearing what they want to hear" from mentors/books/etc and pick out things like "focus on the experience", "leverage network effects" or the dreaded "get a distribution partner" instead of simply finding customers who would immediately start paying for a solution to their biggest problems.