If you remember lyrics to songs, or words for a play, easily, you may not understand that others find this more difficult than you, or in extreme cases, virtually impossible.
This does not mean that they do not wish to sing, or that they are any less interested in doing so than you.
Is it possible that you may come across as smug, or "holier than thou" in your entrenched position?
A little bit of give and take might go a long way to make the singarounds a less intimidating experience for the nervous, but nevertheless, keen performer.
In my limited experience I have seen intolerance and bad manners expressed in looks, actions and comments at singarounds and festivals over the years. They would have been happier and better places without it, in what is after all, a hobby for most.
However, these occasions are infrequent. Most go just to have a good time enjoying the fun of singing and playing together in an acoustic setting.