Architecture, at the theory level, has a clear sense of its cultural purpose - how shaping space (through function, aesthetics, process, materiality) shapes social interactions and all the follow-on effects of that.

Maybe its just too young, but design in the context of tech doesn't feel like it has this sense (an internal theory of itself), despite its products having as much or more influence.

Not many manifestos about what an app *should be*, or maybe I'm not plugged in

Sounds like a good place to start writing! I have some thoughts myself if you are interested in a collab.