Interesting, it's enabled for me -- that's how I bought it -- without creating an account. Maybe this feature is perhaps region locked somehow? I'm in UK.

EDIT: it is indeed gated by some vague heuristics[1].

>Buyers don't always have the option to complete their purchases without using or creating a PayPal account. This option is presented based on several risk factors, including but not limited to the buyer's PayPal purchase history, PayPal cookies stored on the buyer's computer, the buyer's location, or a credit assessment.

[1] https://www.paypal.com/uk/smarthelp/article/how-do-i-accept-...