After moving the region files created using bobby into a single player world, when you load the world all chunks get regenerated, if spectatorsGenerateChunks is set to false the chunks just don't load.
The log just says
[23:32:53] [Server thread/ERROR]: Chunk file at [X, Y] is missing level data, skipping
for every chunk loaded.
Opening the world in minutor or amulet does work properly.
Using bobby 2.0.4 and Ubuntu 20.04.

Bobby is not a world downloader. It uses region files as the storage medium purely for convenience and so no extra code is needed to load from a fallback world. There is a lot missing from bobby's cache that would be required to be able to load it as a regular world.