Time in market.
Whilst JavaScript has been around since the late 1990's it has traditionally only existed in the browser; and the performance was nonexistent. It wasn't until Google created their V8 JavaScript engine and someone went "let's make a standalone" -- aka node.js -- that it was even practical to use as a general computing language. There are STILL developers who don't even realize you can use JavaScript server side, and an equal number who STILL scoff at the mere notion since prior to node.js it was one of the slowest hardest to use inefficient languages available.
Basically, node.js came out in 2009, it took nearly five years for it to gain any real foothold with developers, and prior to that NOBODY looked at JavaScript as anything more than a browser based novelty. It is STILL considered by many a rinky tinkertoy. Though that reputation is undeserved, the stigma of its past persists!
Python came out in 1991. It has for all intents and purposes a five year head start on EXISTING as a programming language, and a 18 year head start on being used as a general purpose computing language you can run directly on a system without a browser.
It's hard to overcome that type of traction.