Discussion is pretty much moot - JNC has chosen a payment processor (I think they said it was Stripe) that suits their company needs, and that processor is a competitor of PayPal. Because of that, they don't do PP transactions. To convert JNC to PP, you would have to convince them that PP is better than their current processor.
I know several people who have used both Stripe and PP on the vendor side of the transaction. I am told PP is too much of a pain to deal with. Even if you use a payment processor that accepts the PP transactions, your PP account can be frozen by PP at any time, for any reason. Have fun getting any money you left in your PP account when that happens.
I really don't know any of them that stuck with PP, unless they were selling on eBay.
If you've made "Accepts PayPal" an integral part of your online life, several retailers of JNC books accept it, and you don't HAVE to be a member to buy JNC books.