I think the pass may have been great for Forza too. I remember I previously saw the sales for the series had been declining due to MS releasing a new game almost every year (they had quickened up the pace), and the latest one had even worse sales when it first released. Yet despite this, it became the most played one in the series, and that seems to have been thanks to the pass. People didn't seem too hot on buying a new Forza so quickly after all the others, but with how cheap the pass was, and the game being in the pass, it made it very attractive and became more popular as a result. There's no denying the game itself was great, everyone seemed to agree, they just felt tired of buying a new one so often.That is what happened to me too as I have tested many games I would probably skip.
Having a pass is also good for scenarios like this one, where a game might be released yearly (like sport games) and seem "expensive" as result, but then end up much cheaper if it's part of a subscription package. Then if they want to keep it outside of the pass, they can buy it forever instead.