Because the electronic shutter has the rolling shutter effect, image would be skewed when panning camera. I think that’s why it is disabled.
You’re probably correct, but should you really be shooting while panning anyway?
Fuji seems to encourage it by putting the pano mode on the drive setting dial ;-)
Frankly, with the limited image quality you get doing panos in-camera, your are probably better off just using your phone.
I tried it and the quality seems pretty good, definitely superior to my cell phone. Granted, owning a good camera allows me to save money for my phones, so I don't have a state-of-the-art smartphone camera. :-D
A current run of the mill iPhone will produce higher resolution panos than your Fuji will in-camera. The best way to do a pano is to take high quality individual vertical shots (NOT while panning) and stitch them together later. The in-camera method is fine for quickies, but it doesn’t begin to compare with doing it “the right way”.
I have done stitching before, and it is a fair bit of work to do it "the right way". I don't normally have a lot of time for shooting during my travels, so it's nice to have the ability to do a 'quickie'.
To be fair, the 9600x2160 resolution from the X-T30 is sufficient for my purposes. I am more concerned with the noise and the stitching however. Apple does a better job at stitching I believe.