You can't blame this on the developer of Lukla: this is how IPACS has designed it! JustFlight also installs its plane into that folder. So this is how it should be, at least according to IPACS. So Sasa did everything by the book.
Thats BS, sorry. They are using the windows standard document storage as their addon repository. Thats not by the book. And a few other vendors did this too. Microsoft deliberately designed a folder structure for this. This is what you have to follow by the book.
\%USERPROFILE%\AppData, this is where worst case, user bound program data goes. ORBX does install there, their program data. This is by the book.
\%USERPROFILE%\Documents\ this is where user documents shall end up. This folder is synced with the cloud in a lot of cases, same for pictures, same for videos. Config files, OK, Logs OK. This should never contain program data.
There were some hefty discussions with certain other sim vendors that all of a sudden pushed to install there. Meanwhile this has ended up with changing the installers and leaving the config files there. And this saves storage on the user profile drives, keeps cloud sync rate low and does not mismatch locations.
IPACS or whoever, should stick to M$ design. Thats a very fundamental thing. Another fundamental thing is that the installer shall have a choice on where to install. This is not just related to AFS but to all. Not everyone has a C drive with all on it. Some do have more than one drive!