For one simple reason:
I am a schmuck off the street who never once considered going to a conservatory or studying music formally.
You are a conservatory or music school kid who can probably look forward to a life of auditions and professional performing.
And yet, because I play a piano, I know a ton more music theory than you do. And I mean, a ton.
That is why you need a piano qualification.
Now put down the flute, pull up the fallboard, and get to work.