I think of choices in VNs as like routes from point A to point(s) B (,C,D,E...)
That is, it's a collection of paths from beginning to end. It's like if I wanted to get you from starting town Foopsville to an ending town in another country, Foobia. I build you some different highways and tunnels, and you get to choose which path you will take. Your experience will be different depending on which highway you take. That certainly gives you more choices in a single trip (playthrough) than if I just made it linear where you get one highway from Foopsville to a single destination in Foobia (single ending.)
I suppose you could argue that the choice is an illusion created by making the game "big" and only letting the player experience one path in a given play. That's true to an extent, but if you look at things that way, there's no game that gives you true "choice." I mean, even chess has a finite number of moves, as does a pure classic game like Super Mario Brothers (excluding -1 glitch world repeating which would open up an infinite number.)
It's all about the experience you create for the player
VN choice also lets you experience "what ifs" that let you learn more about the characters. How would they react in this situation, what would have happened if I did this, etc.






