Modern JavaScript is not a very badly designed programming language. It's a good, productive programming language. Most of the quirks can be disabled with a linter, and optionally a lot safety can be brought in with typing (using e.g. TypeScript).
On the other hand, many developers don't know much about programming and JavaScript, and therefore tend to have unjustified criticism of the language.
JavaScript was a perfect choice for Node.js. It's event-driven design is a perfect fit for a performant web server. Python would have been a bad choice, because it didn't support asynchronous programming when Node.js was created. Furthermore, using the same language in the backend and frontend will reduce context switching, enable code reuse and generally speaking improve implementation efficiency.
On the other hand, many developers don't know much about programming and JavaScript, and therefore tend to have unjustified criticism of the language.
JavaScript was a perfect choice for Node.js. It's event-driven design is a perfect fit for a performant web server. Python would have been a bad choice, because it didn't support asynchronous programming when Node.js was created. Furthermore, using the same language in the backend and frontend will reduce context switching, enable code reuse and generally speaking improve implementation efficiency.