Realistic Zelda sells better than cartoony Zelda....
.... that's why we're making a cartoony Zelda.
Jokes apart, it seems like a bit semplicistic conclusion. I believe sales of well established series like Zelda are very well connected to fan expectations and the ability to attract new users.
Of course if you are planning to make a very traditional game like TP you should go for a more traditional artstyle (one that fans are accostumed to), if you're planning to attract new players a cartoony artstyle is not a wrong choice by default, depending on other design choices as well.