It's only convenient because I already use Paypal.

I only buy maybe 2-3 games a year from Steam directly. Most of the games in my library are from humble bundle (or similar sites). It's just been easier to click the Paypal button for the occasional impulse buy than to track down my wallet.

I'll probably go ahead and put my CC details in now that I know Paypal carries risk.

It's been several years since I used a card on Steam, but IIRC I had to regularly re-input the card details, whereas I rarely have to re-log into PayPal.

Cards expire every few years