* Would you hire somebody who wasn't able to learn a new language in a reasonable amount of time?
* Would you let somebody who just started with PHP (by virtue of it being an easy language to start with) work on your backend?
* Would you hire somebody who wasn't able to learn a new language in a reasonable amount of time?
* Would you let somebody who just started with PHP (by virtue of it being an easy language to start with) work on your backend?
A good developer will learn a new language in a reasonable amount of time and will be able to be productive and write good code in it.
A PHP-only (or X-only for that matter) developer is, by the definition above, not a good developer.
So why restrict oneself to some random pool of X-only people?
FWIW, they have released cool open source projects on Haskell and ocaml, so it's not like they've never considered any alternatives.
I also have a small suspicion that they wanted to stick to their roots a bit. But thats just me.