They simply thought that they wore out this theme.
Despite my best efforts, I keep seeing this pop up around the net.
The simple fact is that Iorveth originally had an important role in the game, and they did promise during the 2013 Game Informer reveal that he would be in the game. He had a big role in a massive questline that involved the Nilfgaardian's war effort and an outbreak of the Catrioana. He would have teamed up with the Temerians (Roche, Ves and Thaler) and Geralt to get the cure, as the plague was wiping out his guys as well. This questline was the original implementation of HoS, before it was completely rewritten for the expansion.
The nonexistence of Scoia'Tael in Witcher 3 is something i will never forgive CDPR.
I feel you, man, but remember that the people who worked on the content didn't want it to get cut. There simply wasn't enough time. From what I've heard, the people who were leads or heavily invested in this particular quest line still feel pretty shitty about it not being in the game, but there was nothing that they could do about it.