You should see the average percentage of people who finish a whole TV series on Netflix
I think that is the problem inherent to Starfield being on GamePass.
You're devaluing gaming, so you don't feel inclined to finish the game. You didn't pay for it outright.
On top of that, you're getting a lot of people who aren't necessarily interested in the genre, who end up disappointed with it.
If you had a lot of people play Elden Ring for free, the vast majority of people wouldn't play it for more than an hour or so. I'm sure there were a lot of people who bought Elden Ring and had never played a Souls game, and either returned it or stopped playing it.