Why am I using IOS 9, you ask? Because that is the latest my device supports. Why not upgrade you ask? Because my device works fine and is in great shape, so I'd rather not destroy the planet for for that sake of my own greed, vanity and stupidity.
a) you are running on a platform that it is impossible to load a previous OS onto an actual device, so if the developer bought their device after iOS 9 (quite likely), that actually can't put iOS 9 onto their device for testing.
b) would you excited about testing 4 years' worth of operating systems over at least 3 devices (iPhone 7 size, iPhone big size, iPhablet size), many of which you can only do on the simulator ...
c) ... fixing bugs on obsolete versions of the OS that few users will even encounter because they cannot run those versions
c) ... for free
d) ... just to accommodate 1.5% of users who insist on living four years in the past?
If you are the kind of person that likes to do all that for free, though, perhaps you could offer your assistance to the author?
Btw, Apple will recycle your old phone for free, if the planet is the only thing holding you back.
[0] https://gs.statcounter.com/os-version-market-share/ios/mobil...
If it doesn't work for your setup then just move on instead of telling people to spend more of their time to make it work for your edge case.