Basically, why popcorn? Why not something else? And what made people stray away from the drive-in theaters to indoor ones we have today?
There's always room for discussion, but perhaps these previous topics will answer your inquiry
How did popcorn become the staple food of the cinemas (and eventually an accompaniment to the home cinematic experience)?
When and why did popcorn become a popular and common movie snack?
When did the eating in cinema appeared? Was popcorn created for this purpoise? Was there anything similar before in theaters?