I've done about 100 published games. After doing so many games something happened to me regarding how I see the games.
I see a game as a bunch of components / features we want into the game and these all depend on each other. See also
We want to have all these great features but somewhere is the reality of time. Somewhere we need to divide which components are in and which out. How easily they drop to the out part is to do with their priority.
Most the priority features are the ones you'll never drop - these are also your core.
Here in this sample game we might realise during production at some point that we cannot do the storyline, it's just too big. What can we fit if anything? Maybe Multiplayer? No, that require more additional supporting features, but we have some achievements and those would support the core gameplay so let's do that!
So this is what happens in the designers mind during production. Each feature is prioritised based on