Simple reason: Because the package is not optimized for that.
It can be shrinked more, but that needs help.
And I must confess, I rather spend my time on bug fixes than space optimizations.
BTW, any idea how Kate is so fast? Is there an architecture explanation somewhere? Is it based on Scintilla? I'm on a block editor[1] in Qt C++ and QML so that kind of information will be helpful.
If I’m not mistaken, you also contributed to my own Notes app https://github.com/nuttyartist/notes, so thanks!
Can you please point where in Kate’s source code I’ll see the implementation for this? That would be super helpful.