Found this old post by Jon Skinner on why SublimeText went with Python.
If you’re building an application, then your users will get much more out of it if you given them a plugin API. For Sublime Text, I settled on Python as the extension language. In fact, I think you’d be mad to choose anything else.
It’s well-reasoned, and considers all the alternatives at that time.
However, it’s also clear how, 14 years later, the landscape favors JS/TS as the scripting language for an editor/IDE like VSCode.
Lua is another candidate, which has a lot of uptake in games. It has a very small code footprint, and excellent runtime speed. However, its paucity of libraries, weak Unicode support, and small-medium user base make it hard to justify as an extension language for desktop applications.
Ditto for Lua in Neovim today.