These big companies are doing this for bragging rights and to reverse engineer other companies technology. They have unlimited cash flow and time to do so. Just like every other industry, cars, electronics, food, etc., but they cannot publicly release there findings to the public unless they want to get sued by the copyright holder of the product they are reverse engineering.
Even if a leaked driver set made its way to the public it would be obsolete before it was ever released so what would be the point. If you never want to update your drivers then it would be cool I guess.
