zip-file-as-a-container-format seems pragmatic: it's a way to bundle multiple files into one file (easier to manage than scattering multiple files), it avoids introducing a new proprietary format, it can optionally be compressed, support for reading and writing the container format is already widespread.

To give two examples of prior art, it worked for Quake 3 data files (.pk3) & geospatial data files (.kmz)

Maybe it's not the best choice but it doesn't seem like a bad one.