Actually, you may pay with crypto, as mentioned in the FAQ under “I want to pay for premium membership but cannot or do not want to pay via PayPal.”
It’s just that the process is manual because I have not taken the time to make the necessary modifications to the website to accept crypto. If you think about it, for a business, there is no real advantage in accepting crypto at this time (2019). Also, PayPal gets a lot of bad rap these days but it actually works pretty well and there is existing integration with the membership plugin I’m using. Recurring payments are another thing that is not possible with crypto (although there have been talks about adding such a feature to ethereum).
If you like, you can select the plan that you would like to pay for, convert the USD amount and send a transaction to one of these addresses: