Because all the other Loud sisters can be described by what they're the best at.
Luna is the best at music.
Luan is the best at comedy.
Lynn is the best at sports.
Lisa is the best at science.
Leni on the other hand, is a bit of an idiot, but that's what makes her endearing. We rather see her try to succeed and fuck up than effortlessly succeed without trying.
This is why it's more amusing to watch Homer sit fire to a bowl of corn flakes than it is to watch him successful make the best damn breakfast Mr Burns had even eaten.