Nobody should!
Each to their own.
From my perspective nobody has ever been able to explain to me how its possible to drop a brand new £1200+ phone on a tiled floor
To anyone who routinely drops their phone, a case is an essential thing. Of course many out there see their phone as a tool and don't really care about scratches and dings but I cant relate to that id always keep my phone in good condition.
Ive never dropped my phone. ever. Some say thats a lie but I promise you it's true. How? Do I have magical powers? Am I a rubbish member of the X-Men whose mutant power is to keep hold of something in my hand without dropping it? Maybe. What I do know is that when handing my phone I give it the appropriate amount of care given its value and therefore would never drop it.
As an adult with average human motor skills I am quite confident holding and using my phone without the thought or worry of dropping it in the same way if you handed me a Vase or a Glass that I am 100% confident I won't suddenly drop it on the floor.