My theory, as someone admittedly inexpert in both Lisp and Haskell but having used both on occasion, is that both are so ridiculously powerful in different ways compared to "normal" languages that very few people ever even reach the point of being comfortable Blub programmers in either, never mind hitting the wall and wondering "what's next?" [0]

Really, how many programmers are out there who simultaneously 1) spend enough time with either language to master it 2) are smart enough to not only realize the language is limiting them, but to invent a new language to surpass those limits 3) aren't heavily tied to their current language 4) have enough spare time to bootstrap a new language with all the associated scaffolding (libraries, &c.) needed for anyone to want to try it?

[0] Feel free to substitute Scheme, an ML dialect, or other related languages into that sentence.