I think that's related to the high fault-tolerance in Javascript. A good developer is good in any language, so she can work with Javascript. A beginner or even a bad developer can make things happen in Javascript, when that is not always possible in other languages. So the entry point level is so low that a lot of people is using it.
> Other platforms are not very 'hackable'; why is this?
I prefer strong typed languages. I use TypeScript when I have to do some JS work as it is easier to maintain in the long term. But that means that you need to know what you are doing before starting to do anything. Compile, fix errors, repeat.
I can see that for starters JS is more fun and "hackable", as it was BASIC for me when I started.