Well it's all about money, as much as i love the saga of the witcher, it's very transparent that the author is a greedy person, because there was a time he loved the game until there was a money dispute.
We want authors of our favourite books, games and films to be nice people. We imagine them so based on the product we love.
As much as it pains me to say it, Sapkowski is not just greedy. He's an altogether unlikable (swear filter) person altogether. He's incredibly arrogant and thinks himself to be the best fantasy writer on the planet. He was alright as long as people loved his books. The problem he has with the games is not just that he didn't get paid enough. After all, he got his due, eventually. (After a lot of screeching, kicking and general arsehattery). His main problem with the games is that the general notion switched from "Ah, The Witcher, amazing book series" to "Ah, The Witcher, amazing games based on that nice book series".
His books play the second violin in public opinion, now and he can't stomach it.
So I think he jumped at the Netflix adaptation as something that will overshadow the games and something he can, once again, have his name on.
The way it's going though, I'm not sure if that's what is going to happen.