I don’t think that spam is a fair comparison. Spammers send out offer for stuff that people want. It’s completely different than first giving out what people want and then asking for a gratitude payment.

Spam’s success rate would be dictated by the percentage of the people who want the product in the general population after passing through the spam delivery funnel.

With the donations it’s completely different mechanism.

Nevertheless, the fallacy is that small looking number of market share is the smallest possible market share.