That chart shows the number of "essential patent families", not their relative importance. It maybe that the 3 most important patents, or 3 more important families, are held by Nokia, Ericsson, and Qualcomm ... but that Qualcomm just doesn't own _many_ of those patents.

(heck, for all we know, the 3 that Qualcomm owns might, alone, be the 3 most important)