Why do you think they owe you this? You didn't pay them, and they didn't accept a contract.
When you make something that people use and like and want to improve, you should at least have the common decency to tell them beforehand: "this is my show, not gonna accept PRs".
I don't think it's such an exhausting job to write two lines at the top of the README.
I’m grateful just to see the code and choose to use it, or not. If I think some random volunteer should do something, I’ll attach that suggestion with some money or a contract or at least a beer.
What I love about open source is that it’s a big place that has lots different people. It’s beautiful because someone can write code and never talk to anyone and their code is still good and useful.
Maybe a better, more truthful statement is “OSS maintainers will have better engagement with the community if they proactively manage expectations.” And if the maintainer cares about that, it will apply. But I think there are quite a few projects that don’t really care much about community.
The OSS maintainer should clearly, upfront, preliminarily, outline how do they govern the project: how much are they open to change the project's core values, how responsive on average will they be in terms of opened issues and PRs, roughly how often would they engage in technical architectural debates -- stuff along those lines.
I feel many people get toxic if they had unrealistic expectations -- and that's of course not okay.
But IMO the OSS maintainers can be a little more preliminarily proactive in managing expectations from earlier stages.