You're comparing world wide numbers of Netflix to US only numbers of CSI.
"CSI: CRIME SCENE INVESTIGATION gathered more than 73.8 million viewers worldwide beating out last year's winner House. CSI previously won the International Audience Award in 2007 and 2008"
I'm not saying ST isn't a massive show, obviously it is, I'm just saying it's not as a crazy diff'rence like you're thinking.
And let's not even get into Netlix's viewership numbers that I don;t think anyone believes.