/u/Inconceivable's answer is spot-on, and I would also add that some people might pay for more... well... quality.
I subscribed to one of these sites several years ago, and there really was a difference in quality. I knew I could go in and that I didn't have to spend half an hour to find a good video. This is even truer today, since the free sites' selection has grown less and less desirable (not really the word I'm looking for, but you know what I mean...).
/u/Inconceivable's answer is spot-on, and I would also add that some people might pay for more... well... quality.
I subscribed to one of these sites several years ago, and there really was a difference in quality. I knew I could go in and that I didn't have to spend half an hour to find a good video. This is even truer today, since the free sites' selection has grown less and less desirable (not really the word I'm looking for, but you know what I mean...).
Huh. I guess that makes sense then, if you're going for quality over quantity.