Forgive me but lets 'scale' game purchases that cost the consumer/gamer $20 & $40 a title. Without going into retail/distro shares of the take we get:

Game A @ $20 a user x 500K sales = $10M, x 1M sales = $20M
Game B @ $40 a user x 500K sales = $20M, x 1M sales = $40M

Assuming the 'Game Pass' will cut into if not eliminate most/all Xbox & PC game sales, ether multiplatform releases (Playstation & Nintendo) that compliment the assumed single lump sum from Microsoft or very low production costs to offset the lost income from single game purchases might be in order.

One might assume that if a game cost "X" to develop and Microsoft offered you "X+%yy" (some fixed percentage profit on your development investment) that some might go for the locked in profit/ROI vs taking their chances on the open market.