The airport excluded are not "random", you surely had them installed at one time and what you excluded is kept in the \Addon Manager\MSFS\fsdreamteam-gsx-world-of-jetways_backup folder, this so if you took lot of time carefully select airports to exclude, we save your choice there, so you won't have to do all the work again, in case you reinstall GSX.
So, if you ADD a new airport to the Disabled list or run the Exclude routine again, it will just ADD the new airport or airports you installed since the last time you ran it, but it won't remove the ones that might not be installed anymore at this time UNLESS you explicitly move them back to the Enabled side.
If you want to start from scratch, just remove the \Addon Manager\MSFS\fsdreamteam-gsx-world-of-jetways_backup folder, so the Disabled list will be empty again.