Posted 16 July 2016 - 12:14 PM
Consider it from their position.
They have invested all of their careers, their lives, they have built this brand. It started as nothing, it started as ideas that they had, and they invested everything to turn it in to a successful brand. Now that they have built a successful product, a full world of creative growth, other people are coming in and forcing them to change their own stories. Fans write their own fan fictions, and soon more and more people accept it as part of the world. Even when the product's creators and owners didn't want to go that direction, those external works force a direction. Fans may cry "tell more of this", or "make it more like this book", forcing the product's creators to change the ideas they were working on.
At the highest risk those fan-created works can completely destroy the company. A badly-timed fan release immediately before a product launch can sour the launch, or make the world less receptive to the products. Fan-created works can ruin a story line or a product idea that has been planned for years. Fan created works have the potential to increase the product's value, but they also compete with the product and have the potential to destroy much of the value. Fan-created products are dangerous.
Most big brands will quietly ignore the tiny fan fictions and small fan products that stay within the fan community because as long as they are small they are mostly a positive influence, increasing brand awareness and keeping the fans active among themselves. They are never fully acknowledged or made legitimate, because someday a fan-created product may do something that goes against the product creators plans. The fan's works may someday become popular in their own right and grow beyond the fan community. The fan's works may start to eclipse the real product, the fan's work may take away value from the original work. And when that happens the product owners need to step in and say: "No. You cannot do that. This is our product, our ideas, our worlds, our creations. You cannot have them."
If you approach them as a fan, telling them that you are going to make a product using their product lines, you are presenting yourself as a threat. They will shut that down. Such fan-created products threaten to destroy what the product owners have invested their lives to create. The product owners (correctly) see it as a huge risk to their very core with practically nothing to gain from permitting it to grow.
However, when businesses approach as a business opportunity to help build and expand on their products and product lines, there is a chance the company will listen. They will probably shut the proposal down and say "no", but there is a chance they will listen, perhaps finding a way to work it in with their plans, and perhaps eventually say "yes". The more power or creative control granted to the product owners the more likely a deal can be struck. Normally this includes a truckload of money and a contract that says the product owners get final say on all creative aspects, they get a say in all marketing, in all branding, and in all other uses of their product. In exchange, the other company can build around the product to make their own money while supporting and building up the brand.
The people over at Games Workshop have invested roughly 30 years turning their ideas into an enormously valuable product line. They have turned their ideas into a product with a brand equity in the hundreds of millions of dollars, perhaps a brand equity reaching to billions of dollars. (Note that brand equity is very different than a company's cash value or stock price.) There is no way they are trusting this incredibly valuable brand to someone unless that someone brings something of incredible value back.
It seems you are only considering this from your position, the position of a fan of their work.