My assumption is the numbers don't work out for smaller AAA games (2-5 million sellers). GamePass models works on the premise that the average gamer spends less than $120 a year on videogames. So basically your average casual who spends $60 per year on Call of Duty or GTAV or FIFA would now be spending $120 and playing more games, which is great for the industry's overall numbers.
Problem is, smaller AAA games like Resident Evil or Devil May Cry, are likely purchased by people who spend maybe $200 or $300 a year on videogames. If they're only spending $120 a year now, how is this amount of money supposed to cover for the $250-300 they might have spent in a given year? (CoD, FIFA, RE ,DMC, Dark Souls, etc)
The way I see it, Activision/Electronic Arts/Ubisoft/Take Two aren't going to accept anything less than the $$$$ they currently make every year selling their games for $60 per copy, so basically smaller publishers are going to get boned in terms of how much they get from the licensing of their games to MS/Sony's game passes.
Oh and if they choose to not put their games on gamepass, good luck selling them for $40-60 when games have been devalued to "all you can eat" entertainment. Most people don't even feel like spending $12 to go see a movie nowadays because of Netflix, imagine trying to sell them a game for $60 when they own a GamePass that features the majority of the big AAAA releases.