It's open source software created by a volunteer. Using the latest version of Python lets me leverage features which help me focus on the problem at hand. f-strings, pathlib integration, the latest typing module, and so on.

I'm sorry this makes using my tool harder for you but I'm sure there is an easy way for you to install Python 3.6 without destroying your system Python. There's Homebrew for macOS, deadsnakes for Ubuntu, EPEL for RedHat, and so on.