AbdulAlhazred
Legend
I will try again, trying to build on what @Arilyn posted.
If the thing that a person enjoys in RPGing is a sense of being in the GM's world, then why would you explain that in terms of agency? The notion of audience membership seems like a more fruitful starting point.
I enjoy going to movies, and I enjoy listening to music, but I don't explain that pleasure in terms of my agency.
If the purposes of worldbuilding include establishing material for the GM to present to the players, is anyone interested in explaining why that is worthwhile?
If the purpose of worldbuilding is - in metaphorical terms - to give the players stuff to interact with via their PCs, which means - in literal terms - to establish frameworks for declaring actions which then affect the way the GM narrates his/her setting - is anyone interested in explaining why that is worthwhile?
I think the proposition is that someone, a 'GM', provides a box full of toys, the 'sandbox' if you will. The players are then challenged to essentially build whatever sort of castle they want with the pieces parts provided. Its like Lego where you wanted to build the Starship Enterprise, but maybe you got the Castle Set for your birthday!

Honestly, I'm being a little bit silly here, its midnight, but this is clearly the idea, that you have a set of situations and 'things' that make up the world, and the entire activity of the players is in MANIPULATING them, not in 'being told about them'. I think this IS a mistake you make in your explication. The activity of DOING STUFF is what is primary (at least for some players, this is where the old 'WotC player types' thing comes in).
In Story Now, its doing stuff with a focus on your story/conflict and with a goal of character growth and interesting narrative resulting. In 'classic' play the activity is just more concrete and working with a more limited set of elements (maybe, truthfully it might not turn out to be so).