Being able to accept credit cards directly means a website would have to set up a merchant account with all the various credit card companies and pay to use their credit acceptance systems. Security and a system of accepting credit card details would have to be coded. For a non-commerce website that would be way too much effort.
More and more website are getting hacked and ensuring that a website is secure enough to store a credit card details is just about impossible. Let PayPal take care of the security. Using PayPal means a website does not get to see your credit card details at all. If a website does not have your credit card details stored then when it inevitably gets hacked there is no important information to steal.
You may be slightly pissed off about not being able to directly enter your credit card details on a website but I guarantee you'll be even more pissed off when they get stolen.
PayPal invests a huge amount of time and effort to make their payment system secure and easy to use, it's their business. XCSkies does weather, not payment security.
Create a PayPal account, it's easy. Or give your money to someone with a PayPal account and let them pay your XCSkies subscription.
Dave.