Famously, as with many other things in computer science, writing a toy programming language that can compute Fibonacci is doable in a couple of hours, but writing a usable programming language that needs to stand up to real programs for users is typically somewhere between a decade and a lifetime of work.

If he'd announced the language twelve years ago and then not touched it again until a few months ago I'd believe you. But there's plenty of documented evidence that he's been spending a bunch of time on it, and (allegedly) even using it in his commercial projects.

Not to say that he's been working on it full-time for 12 years, of course, but even allowing for part-time work that's far beyond the initial ‘easier than The Witness’ premise.