Because Overbuff is broken and completely unreliable right now. Read my post about it for more info.
It’s actually been broken for seasons now. It got really bad around the time champion was added.
Neither are picked that much in top 500 right now. See my post for a breakdown of pick rates based on the PC Americas leaderboard. I know you are a console player so I’d actually expect them to be more picked on console, but still.