[foldr]

Primarily because there is no evidence that the challenge exists, and it's hard to imagine what it could even be. Chomsky's own research interests didn't really lend themselves to setting some kind of math olympiad style 'challenge'. If he was excited about setting up prizes or challenges in linguistics, you have to wonder why he never once did it. He certainly could have if he'd wanted to.

[basedrum]

Just because you can't find it doesn't mean it didn't happen. Also just because you give it hard to imagine, does not mean that it didn't happen, or that people with better imaginations as you could accomplish that.

[foldr]

I was a generative linguist in my previous career and no linguist that I know has ever heard of this Chomsky challenge thing. It’s hard to prove that something doesn’t exist, but I’m fairly sure it doesn’t.

[basedrum]

He could have created this, and then Epstein decided not to launch it? It can exist without you and others knowing about it.

[foldr]

It's conceivable, but I doubt it, for the reasons I mentioned. If Chomsky created this thing then presumably his wife can dig out some kind of record of it (as she apparently handled the communication with Epstein's office). So far we haven't seen it.