I guess no-one had time/motivation to write it suitable for TPT++, but I'm not sure, though.
That is kinda stupid since there reads this on FAQ: "How do I use floodfill/prop/another tool? Check the wiki or README - they have good descriptions."
A new README just needs to be written. And it can be almost exactly the same too, the only things that need to be changed are the hotkey section, (maybe the command line arguments too), and the Changelog.
But things need to be added to it first, like a better tpt description. The one on the download page might work. Maybe a note about it being tpt++ too.