> Swiping from random directions achieves different things (and how would you even know you can?)
Cultural context, the same way you'd know tapping on an icon opens an app.
No, tapping something visible and seeing what happens is discoverable. And Apple used to have skeuomorphism to help with affordance. Swiping from various directions and other hidden shortcuts aren't discoverable, and my guess is most users can't find half of the features of their phone.
Tapping something is discoverable and a basic human instinct. How the hell do you discover "swipe up from the bottom edge and then slightly right" to open the app switcher?