1. Gorgeous high resolution, high refresh rate, generally pretty screen.
2. Long battery life.
3. Instant wake.
4. Ruggedness. Even with solid-state everything I'm always a little wary of chucking my laptop into the passenger seat of a car, taking it near sand or dust, etc. There's fan vents and hinges and... stuff. The iPad Pro in a Logitech Folio case has all the corners protected from drops, no airflow, few holes. I just don't worry about it.
5. Pencil. The handwritten notes experience has gotten really good. Being able to flick into that mode any time is nice.
I wonder though on vnc via ipad, how do you use mouse? I imagine touch support would be an issue in many desktop applications.
The different remote desktop apps (VNC, Nomachine, etc) have ways to translate touch events into mouse pointer movements/clicks. Not what you'd want to use for a serious CAD session, but fine for little things here and there to save pulling out the mouse.