It is the most used GPU. Does not mean it represents a majority of the market.
Lets imagine we had 20 different GPUs only. One was a 980 TI and had 15 % market share. The others were between a GTX 960 and and AMD 7790 in power. Sure, those 19 GPUs will spread themselves over 85% of the market. So each one will have circa 4.5% of the market. The 980 Ti will have 15%!
But... what is the ACTUAL majority?
*I hope the example is easy to understand, as it seems that statistics are poorly understood these days. Despite being extremely easy stuff.