The reason there is a 9 image limit is because drag and drop re-ordering starts to fall apart when not all of the images fit (vertically) inside the viewport.
You can stack image galleries one after the other, and in most themes they will appear as 1 image gallery on the front end, which is an easy workaround.
Removing the 9 image limit will require completely redesigning the drag and drop behaviour of the gallery card, which is certainly possible, but there has historically been very little demand for.
If anyone wants to get involved as an open source contributor on GitHub and help make it happen, then it will probably happen. But if nobody is contributing, then there might not be enough demand from the wider community at the moment to do the work needed to make this possible.