Perhaps because not everyone is doing development on KDE?
The Ninja-IDE supports linux, windows, and osx so it has broader appeal.
The Ninja-IDE supports linux, windows, and osx so it has broader appeal.
Admittedly, a lot of the download size comes from additional dependencies, but still - I don't want to have to install all that when I use an entirely different WM, and there are alternative WM-independent solutions to begin with.
As for alternatives, I'm not aware of a Python IDE with comparable abilities for Linux (Wing probably comes closest, but is proprietary).
What has the potential for greater impact on your productivity - 320 MB of used disk space or a useful IDE?