Credit cards are basically a financial means of making loans. It is rare today to finds a credit card that offers a true joint account. Most credit cards have one account owner and they share use of the card with authorized users (Apple calls them Participants). AU’s have spending (borrowing) privileges, but zero responsibility for payment (at least in the eyes of the bank). The account owner, has all the responsibility for payments.
A joint credit card is more complex, with each owner sharing full responsibility for the total account, not just their portion. Leaving a joint account dissolves/closes the account, and both parties are fully responsible for total payment. Each must reapply for an individual account, with no assurance of acceptance, if they wish another account.
A savings account is meant to accumulate/create wealth and has different regulations and statutes to comply with. Savings accounts have different ways of distributing or transferring the accumulated wealth upon death of the owner.