To create a gallery mod, you have to scan the files, identify where are the interesting scenes and enclose them in some kind of markers that can be processed by python code.
This is reasonably fast and can be done in a few days for most games.
In this game, the file organization is a complete mess, with nonsensical names, no comments, no logical structure. The process to create a gallery mod would be very long and tedious and nobody wants to do that.