One argument I've seen on PayPal is that it some people use the balance as an "off the books" place in family finances.

Stereotypical narrative: The wife will have a fit if she sees a credit-card transaction for an expensive hobby item. But if you just see "PayPal transfer, $300.00", or better yet, nothing because you paid out of a balance you filled up by selling junk on eBay, it has plausible deniability.