Credit cards (and debit supported on the same systems) are more secure than anything else and furthermore if the worst happens you are fully supported as a customer by 60+ years of case law. Frontier will also be supported by a clear and well tested contract with their merchant bank.
None of that is true for PayPal.
Credit cards are free at the point of use. Credit cards also have the global experience of literally thousands of banks operating them for electronic payment for at least 30 years (arguably a lot longer, depending what you say can be compared to the modern Internet.) They also operate under banking law developed over hundreds of years. Most of all, if you are a victim of fraud with a credit card the law is on your side as the consumer BY DEFAULT in a huge majority of companies.
PayPal don't care about any of that and they spend most of their time arguing that they should not be regulated by any of the above and give even more latitude to abuse fees and sit on cashflow. Now that legislators are finally catching up with the situation they have been thrown out of several countries completely.
Because of that if there's a problem with PayPal, neither the financier nor the supplier care - if a supplier uses PayPal, well, that's a choice, but it's a choice they'll have to live with so there's no compensation for anyone in fraud.
FDev have obviously chosen not to live with that risk. Quite right too. It's utterly baffling to me why anyone would choose to use PayPal who do what they like 90% of the time when you could use a credit card with 60 years of legislation support "the customer is always right."