this is the biggest issue to make payment, paypal offers most relevant option to make payment easily on any currency for international, but why some companies are asking to submit card details to there customer because they need it to store these kind of confidential information without any ulterior motive. There are no surety of the security to keep this information secret with companies and their staffs. So I think Paypal is one of the best option, and envato and all other companies should not ask to their customers to provide their card details.
It’s because anyone could use a stolen credit card through PayPal without verification that would allow “charge-back” issues for the authors, to prevent those issues, it’s normal to be requested to provide more information/details to confirm you’re the legit user of the credit card.