And social reasons aren't important? It's classic socially clueless developer mentality to think technical considerations are the only thing that matter.
Nice straw man argument. Pointing out that PHP is used for social/economic reasons is exactly saying that there are considerations outside technical merit.
At the same time, Facebook is a big Haskell user, but that is because of its technical merits. (Simon Marlow works for Facebook) On a back-end technology such as a compiler, the technical merits of the language are much more important than the social merits of finding enough low-skilled/low-paid developers.