I have no doubts about security and avoid giving my card credentials to random merchants it's exactly my use case for PayPal, but I still got account randomly locked several times over 10 years.

What exactly caused it I have no idea, but might be traveling or using VPN. Once I tried to make fairly big $2000 transaction to pay for my new laptop and spent a week re-verifying my identify with them.

There's really no good reason for anybody to be asking people for their credit card number any more. 3-D Secure exists and all the major schemes have implementations.

Given two merchants, I'll choose the one that uses a credit card over paypal every day. At least with a credit card I've my bank _and_ the scheme on my side. With paypal, it's me (and my bank) against the world ...