First, adding more options takes work. People need to volunteer to do that work, and prove that adding more VMs to the web can be effective (there are many technical challenges, like cross-VM garbage collection, sandboxing issues, etc.). People simply haven't shown this is practical yet.
But, people have meanwhile shown that cross-compiling to JS is practical, from things like CoffeeScript to C++. This is opening up the space to new languages, but it takes time and effort as well - again, the speed depends on how many people volunteer to help out.
But, people have meanwhile shown that cross-compiling to JS is practical, from things like CoffeeScript to C++. This is opening up the space to new languages, but it takes time and effort as well - again, the speed depends on how many people volunteer to help out.