A) You’ll have people selling their place in line, which means that those who can afford to take a large quantity of orders in advance can profit from the difference

B) It’s not exactly good PR to order something and having to wait a variable window of time for it to finally arive at your door (see almost all Bethesda merch incidents post Fallout NV)

C) Valve doesn’t operate like a dropshipper. There is no “white label” steam controller being made in china that they can slap their logo on and sell as soon as people order for it. They have to contract volume in advance, since it’s a bespoke product.