Over a certain size it starts to make sense to vertically integrate your business. If you are big, say Apple, creating your own hardware allows you to do better

Over a certain size it starts to make sense to vertically integrate your business. If you are big, say Apple, creating your own hardware allows you to do better and differentiate against your competitors. It may also allow you to cut off resources for your competitors (see for example oil companies). A company such as Valve is probably on the fence on this. They dominate a small segment of the market, but is not really big enough to do something their competitors can't replicate.