This enables different satisfactions. You can still choose all your options but have a working repl or small compiler where you are trying them within minutes.

Also you decide how much in control you are. Want to provide a hand made grammar? go ahead, want the agent to come up with it just from chatting and pointing it to other languages, ok too. Want to program just the first arithmetic operator yourself and then save the tedium of typing all the others so you can go to the next step? fine...

So you can have a huge toy language in mere days and experiment with stuff you'd have to build for months by hand to be able to play with.