Because it's a black box you have to pay for. No source code available? Gitafuckouttahere.
You know Shottr is only available for macOS, don't you? If source code is so important, why do you even bother using macOS?
I wouldn't install Shottr on any of my Linux machines, even if available. Despite it being objectively better than any available alternative. I'd recreate one myself if necessary.
But on a corporate Mac, where 99.999% of executed code is a black box, why bother?