MyBinder uses a typical full Python kernel running on a temporary remote machine. Voila is the dashboard associated with notebooks in a typical remote server situation. (The Voila Gallery examples use MyBinder with typical Python kernels running on temporary remote machines.)
Here Voici is involved. It is using Pyodide that runs deep in your browser on your local machine using Web Assembly. There is no remote machine running the kernel. At this time a Pyodide-based kernel has a lot of differences with how things work and/or limits of what is possible. (Oh wait, you’ve been using Pyscript, and so you are probably definitely aware of some of that.) So the more proper comparison is if your notebook ran in JupyterLite. And even then Voici has some rough edges on its own as the project is still firmly in development mode. And therefore the even better way to make a comparison would be if you knew your notebook worked if you deployed Voici with your notebook to be served via GitHub pages or some other static serving site.
Summary: Just because something works well in a MyBinder session, doesn’t mean it will work with Voici.