As a web developer, I know JavaScript very well. I have already encountered thousands of its idiosyncrasies and I am very good at making it work for me.
Therefore any tool written in JavaScript is automatically easy for me to understand and modify. If that tool could have been more elegantly written in another language, that's awesome for people who know that other language, but it's irrelevant to me. Even if I kind of know my way around the other language, I'm never going to be as effective with it as the language I use every day. And a lot of people use JavaScript every day. This is the reason why people feel the need to solve problems in JavaScript.