It’s probably also related to when a person first encountered JS. If you learned it pre-2015—even if you’re aware of the changes made in ES6—I can see how it would be hard not to view JS as cumbersome. I personally love to use it, but I can’t imagine that would be true without let, const, classes, etc.
Edit also block scoping and arrow functions!
A similar phenomenon is knowing you’re going to need to go back and update some older section of code and when you finally get around to it, it turns out you wrote it that way to begin with. It’s like… I didn’t think I knew about this approach before…