Why are the EXIF tags empty in the orthomosaic?

If the orthomosaic is large, it might be required to use the BigTIFF library. This library is not recognized by all software (in particular the Windows image viewer). As such, the EXIF data is present but cannot be read by some software. It can be read by the GDAL library, which supports BigTIFF.

While the merged orthomosaic might require BigTIFF, the individual tiles do not, and so using the tiles is a workaround to ensure that the EXIF data can be read by most software.