Why should that be the maintainer's burden?
Presumably, the user wants the best for the product and their ability to use the product. So they have a definite interest in documenting a todo list.
It doesn't make sense for the two to be at war with each other. It is no big deal for the maintainer to ask a favor. It's not too big of a deal for the user to decline. There's no need to attack.
I have often dropped a note to the maintainer of a project I bumped into. I'm sure they would prefer a bug report in their official forge. But I don't really use their software except for this one time. I'm not willing to jump through the hoops to create an account in yet another SaaS just to file this one report. Just dropping them an email was a courtesy. But often they don't interpret it that way. I'm perfectly un-insulted if they just delete my note and never "fix" the issue because it didn't come through proper channels.
No attacks. No war. Just well wishes. But I might very likely avoid the product if I'm ever back in those woods. Not out of anger or retribution. Just because I'll remember that the product had at least one sharp edge for my use case and the maintainer was a bit overwhelmed by the weight of supporting my niche use case. That doesn't make the maintainer a bad person or even a bad maintainer.
If they don't want to, that's certainly their right, but it also tells us something about that project.
Volunteering to maintain a project literally does create entail accepting duties, that's what taking on the role of maintainer entails. They are of course free to give up that role at any time, but those duties exist while that role has been adopted.
You can't really say someone has a "duty" without also implying that they have a "responsibility," and thus liability if they fail to execute those duties properly. I don't see how this fits at all for a volunteer. Very few people are going to volunteer for no pay if they're taking on a risk of liability.
Maybe you mean a civic duty? That would make somewhat more sense, but the problem is that there’s no objective standard against which to test performance. It’s completely subjective and will be forever argued—much like this thread. :-)