I suspect that technical matters such as deployment and integration with other components is of greater concern (though I also suspect that the kind of language fetishism which looks balefully on the use of anything other than C as a system programming language has some effect).
Honestly, it comes down to other languages not understanding how sockets, pointers, and memory really work. When you do servers like this, that's all you're dealing with (plus parsing). In other languages they try to hide these things away from you, or just screw up the concepts making them no easier to use.
For example, if you want to parse an HTTP header in Python you have to iterate through either integers, or break it up into smaller strings, or use the really bad tokenizer library. Most languages with immutable strings make fast parsing and "copy on write" semantics difficult, so they're already harder to work with.
Another example is how they screw up sockets. In C sockets are simple, requiring only a few function calls to work with, and then a bunch of error conditions. Everything you get out of them is bytes put into a buffer of your choice. In other languages you have to work with some badly designed OOP layer that makes no sense, exception classes for each errno, randomly sized buffers with no Chord data structure, or an event system like Twisted that gives no ring buffer or state machine functionality.
In the end, implementing the solid core of a web server is just easier in C. I wouldn't want to implement a full blow web app in it, because doing something like a template system is murder (dynamic languages win hands down there). But the core is much easier.
While in general your criticism of network libraries is generally sound, I believe Haskell gives you more or less the same API as C sockets if you want it.
What does "good" mean in this context?
I suspect that technical matters such as deployment and integration with other components is of greater concern (though I also suspect that the kind of language fetishism which looks balefully on the use of anything other than C as a system programming language has some effect).