If the game is terrible you won't play those DLCs anyway. If the game is good you will have reason to purchase the DLCs when they are released.

Pre-ordering is designed to specifically work around bad reviews a.k.a. releasing poor quality games and getting away with it. The publisher is screwing you and you are paying them to.

Big publishers have no other reason to implement pre-orders. It is a shit-game risk mitigation strategy.

Pre-orders also reduce the amount of working capital required to make a game. This is, obviously, doubly important if you're a small company with very little working capital...

Do pre-orders (non-Steam) go to the developer? My understanding is that they stay with the retailer, who will use that to order stock. For Steam, they have to keep some cash on-hand somehow to handle refunds.