I can't speak to The Witcher, but a big part of Willow's problem is the core audience grew up in the 30ish years since it's release, while the show feels like a step backwards. That's not inherently wrong mind you, as maybe Disney is looking to build something for a younger audience. But much like the comic book industry, when you go hunting for a customer base that isn't into your product, at the cost of the one that is, you risk making almost nobody happy. And when that happens, the product suffers.