Apple is also an absolutely enormous company. Even if Valve wanted to lock in prices, they're simply too small for RAM manufacturers to notice on their radar, unfortunately.
Apple has been doing this since before they were an enormous company. When the iPod Nano was in the works, they bought like 3 years supply outright, to block their competitors.
Pre-iPhone and during the mechanical-disk iPod era, they were a very small and vulnerable entity.
Pre-iPhone and during the mechanical-disk iPod era, they were a very small and vulnerable entity.