Hm. There's a couple reasons I can think of that would cause that. Then I have an alternative suggestion as well.
1) REASONS: Yes, there may be a PayPal setting to NOT require a PayPal account to donate. You'll need to check with PayPal on that. Or, is your account registered with the U.S./Canada, or in another country?
2) Alternatively, if you'd like to collect credit cards on your website without redirecting them, we have several other payment gateways that do not have a monthly fee, like Stripe and Braintree. Those would be viable options as well.
Let me know if you have further questions. Thanks!