Hi Linda,
Here are some of my thoughts on all this.
Like you, I manage an ONS (actually a few of them) where the surname is not that common. In many instances I have been the only one who has any interest in it, and certainly the only one working on them. I started these One Name Studies with "open eyes" and the expectation that I would be the only one working on it. But also that I would commit to actively working on them, and not abandoning them, as so many do. If any collaboration does happen then I look upon that as a happy accident and in grateful for it. In other words, I keep my expectations for collaboration extremely low. Why? Because awareness that something exists usually does not translate into active help on something.
This comes from decades of my own experience working on Open Source software projects. There is this type of "funnel" of "users to developers". There will always be more people interested in your project and using it. Less people who are interested in helping on the project, even less who have the skills to help, even less people who have the time to help, and even less people willing to commit to helping. It helps to adopt the attitude that if you want something done, then do it yourself. The idea of "build it, and they will come" really only works in Hollywood movies. Now, having said that, there's nothing inherently wrong with a bit of advertising. But again, keep expectations low.
Then there is the ONS itself. There are many out there that have very little in the way of a project page, nor any kind of overarching focus. In other words, many do not have any goals for what their study is trying to achieve. If there are no goals to focus on then many projects (in my opinion) devolve into stickering profiles for lack of anything else to do. To me that is activity without a purpose. As above, if I'm going to be the only one working on these things, then I need to make sure to make my time and work effective. When I work on these projects I know why I'm doing the work. It's the clarity of having a purpose.
I have been lucky in that I have 2-3 other "active" collaborators on the same number of One Name Studies. Even then, the work is still sporadic. We all chip away at them from time to time. I'm thankful for that amount of help.