Volunteers make things different
When a large portion, or even all, of the work in a project is done by volunteers rather than paid staff or employees at a company, the dynamics becomes a little different than what they are on a typical commercial software project.
You cannot demand or require that someone works on a particular area, feature or bug as they work on the project voluntarily so they will work on what they want, when they want to.
Volunteers that show up while working on your project as part of their paid job most likely did so because they fixed a problem or added a feature that their employer experienced or deemed important. Not because of priorities you might have in your project.
A large portion of volunteers makes it hard to plan and predict how and where the project will go. That is just fine, you just have to learn with and adapt to it.
Be aware that adding money and compensations to such a project is complicated. If suddenly someone gets paid for doing things others are doing out of the goodness of their hearts, people may think of it as an injustice.
"Why should I do this for free when Joe Smith gets paid to do it?"