Frankly, why? We hardly do static linking with anything at all. What good would it do if you could static link glfw? In fact, we don't ship static libraries for anything by default.

Not so, ruby-2.1.1-1 includes /usr/lib/libruby-static.a, a static library (and I've happily linked statically against it, too).
Reason? I can think of a few, for personal reasons, and I think others may find the same reasons to be applicable.
1. Glfw is just a fair amount of wrappers around gl anyways, and to have to install glfw for a single game could be irritating for some users.
2. Portability to other distros; I don't just want my game to be available to arch users and other distro users who use libs as new as us
3. Its just a 4.1mb file, so does it really make that much of a difference to include it?

In fact, ls /usr/lib/*.a | wc -l returns no less than 150 static libs on my system, and I'm certain I'm not the only one with a plethora of repo packages installed including them.

They are only added when there's no shared version.

I thought about this and I decided I won't fix this for the same reason we recently decided not to have other static libraries. I suggest you maintain a glfw-static package in AUR for users with a similar requirement.