Drive day 1 sales, increasing your chance of getting featured as a "hot new release", increasing visibility and trying to ride the recommendation algorithm.

Sadly Steam encourages everyone to do this - if you don't get high enough in the rankings at launch you basically won't make any money, plus everyone on Steam is super accustomed to getting everything at a discount.

Special price for first EA (early access) customers. Steam recommend 10% discount.

It has become customary for early access titles to have an early bird discount