There's also a bit of fear of The Forth Curse. For those not familiar, The Forth Curse is what happens when you make a language trivially easy to extend but do

There's also a bit of fear of The Forth Curse. For those not familiar, The Forth Curse is what happens when you make a language trivially easy to extend but don't write a large enough standard library of functions or procedures for it. Then your extensible language indeed gets easily extended at every site where it's used. The problem is that it's extended slightly differently in each place to do quite common things slightly differently and in wildly incompatible ways.