Because typing on mobile is slow, app switching is slow, text selection and copy-paste are torture. Pretty much the only interaction of the ones OP listed is scrolling.

Plus, if the above worked, the higher level interactions could trivially work too. "Go to event details", "add that to my calendar".

FWIW, I'm starting to embrace using Gemini as general-purpose UI for some scenarios just because it's faster. Most common one, "<paste whatever> add to my calendar please."