Hi,
The unzipped size mostly comes down to the textures, in our case. We have little control over how these are compressed, formatted and outputted by the Microsoft Flight Simulator SDK tools as the packing/compiling process is now completely automatic compared to previous ESP simulators where we had a form of control over the final texture output.
Many factors play on scenery package size with the new sim, but again in our case, it is most predominantly the textures. If we had included a custom satellite image, this potentially would have added 2-3GB alone in size to the package. So unfortunately for some, the new standard is to expect the file size to continue to increase for larger or similarly sized airports from us and other developers' products for MSFS.
Please let me know if you have any further questions.