I agree with what Rollo has put forward, and may I add. Red Bull is a PR nightmare for engine suppliers with their constant negativity aimed at the engine supplier. They have been really vitriolic with Renault, forgetting that they won 8 titles in 4 years because Renault was so strong. No multi national company wants to have a nightmare like Red Bull constantly criticising them and their products, it is bad for business as members of the general public will take what they say as the gospel, and sales will suffer.

So as well as the fear thing i.e RBR beating the factory team, there is the problem of negative publicity as well