The OP is clearly a troll. The question remains interesting, though.
My theory is that Haskell has a lot of usability problems. A programming language is a UI for programmers. Usability issues are always a sufficient explanation for market disappointments in any product or field.
Most notably, Haskell is rooted in a theoretical foundation that's essentially a major subfield of 20th-century mathematics, using concepts and notations which most programmers (a) do not understand, (b) do not want to understand, (c) do not need to understand, and (d) in many cases are not physically capable of understanding (eg, they have IQs As "LYAH" demonstrates, it's possible to teach programmers (or at least a certain subset thereof) to use Haskell without fully understanding it. But this approach has serious UI problems of its own. It's not very comfortable to use a platform whose semantics you don't understand. There's no comparable hidden complexity in Ruby, Python, Perl, JS, etc.
Laziness is also a significant UI problem, inasmuch as it becomes cognitively very difficult to understand and/or control the performance of your program. Typically in UI, when you find one UI disaster you find more - it shows that usability was not a principal goal of the project.
One of the difficulties in diagnosing usability problems of this type is that people rarely complain about them directly, because their complaint would typically be of the form "Haskell made me feel stupid." My guess is that for everyone who's succeeded in learning them a Haskell, there are four or five who tried it and came away feeling stupid. Not a very pleasant sensation.