Taking money from the public isn't simply a matter of publishing a payment address - you need to keep records, pay taxes, answer support requests, provide refun

Taking money from the public isn't simply a matter of publishing a payment address - you need to keep records, pay taxes, answer support requests, provide refunds where necessary, and deal with the inevitable instances of fraud. If you're accepting crypto or foreign currencies, you also have to deal with exchange rates and much more complicated accounting. It's perfectly reasonable for an author to decide that they don't want to deal with that.