Welcome aboard!
Note that in memory, there are only 3 pictures: the base and emissive textures are pointing to the same picture data.
It’s only in the exported file that the picture data are duplicated, because the loader created two different textures. Maybe a fix could be that the loader only creates a single texture for base and emissive, as those are really pointing to the same entry in the gltf file. However, there may be some good reasons to do it as it is done currently, I will let people knowing more about gltf import/export than me answer.
You can also have a look here about this issue: GLTF Exporter : Optimize textures files