Can you ask them to? It's not exactly the same problem, but I have a modestly successful youtube channel, and I get unsolicited email questions seeking help every day, and I personally try and answer all that I can. I've used the following technique and it helped me receive donations to offset the support effort.
I added a quiet but clear call to action my support replies. It's in a smaller font and below the actual support reply, but it significantly increased the number of donations, and it helps offset my support time. I went from getting no donations, to donations on over 80% of the support questions I answer. Maybe this would work for you too.
Here is what I add at the bottom of help questions I receive:
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As you might expect, I get a lot of requests for help. If you found my response helpful, a small donation for my time is totally optional, but appreciated so that I can continue to offer it as a service. http://buymeacoffee.com/boothjunkie