Q: Why not use gift card for family sharing?

Hi Kestelli,

In order to set up Family Sharing the family organizer must have a credit card or debit card to use for billing. See this article -

Family purchases and payments

If a family member, including the organizer makes a purchase and has gift or store credit, that purchase is first billed to that credit. Family members purchases may not be billed to the organizers store credit unless they are the organizer. See this article -

How iTunes Store purchases are billed

Thanks for using Apple Support Communities.

Best,

Brett L