The expectation is that it would not be mandatory (incidentally: it is not for PayPal Express Checkout either: you can pay with a credit card without having to log in to an account).
Well, yes, as long as that credit card is not somehow linked to an account: if it is linked Paypal will simply refuse to let you use it without logging in.
The OP said "have to create an account", not "log in to an account": it is generally much simpler to log in to an existing PayPal account than type in your credit card number, and billing address.