A few points from my own experience: - Competitive advantage. Providing open source drivers/stacks will in many cases provide insight into implementation details you do not want competitors to easily understand. Also, complex software stacks (the generic parts) could be recompiled by a competitor into a "free" stack of their own. Closed source provides a barrier for competitors to entering the market by cheating/stealing.

In addition, all silicon have bugs that you don't always want your competitors to know about by seeing the workarounds in SW. They will use that against you when trying to replace your chip in a product.

- Customer support and liability

With limited customer support resources, you don't want to debug your product for a customer without knowing exactly what code is running. This applies both for the end product and the silicon vendor. As an example - what happens if a modified driver bricks the product?