This is just my opinion, but as someone who has actually worked full-time with Haskell (though admittedly not since 2015), I think a lot of the problem is due to Haskell's awful error messages and, for most of its life, awful tooling.

When a newbie starts using Haskell, they are immediately put off by the fact that the messages are...esoteric to say the least; weird things of `result a0, expected [b0]`, can be offputting, and make things like F# a much more attractive option.

Also, I feel like, until Intero, editor integration with ghcmod was incredibly difficult to set up, and fairly easy to break, to a point where I eventually uninstalled it.

Cabal, while certainly interesting, would end up in weird scenarios where dependencies wouldn't resolve correctly, resulting in "cabal hell".

Stack has greatly improved on all of these points, and hopefully Haskell catches on a bit more, because despite my criticisms, I do think it's a fantastic language and platform.