Why are portrait and macro lenses always fixed?

I went out and bought a Nikon 50mm portrait lens and was wondering, why are specialty lenses like portrait and macro always fixed?

Prime (fixed focal length) lenses offer the highest quality. Lenses used for portraits can be fixed or zoom, however, the fixed focal length lens has a better chance of providing the best image quality (sharpness, various aberrations, distortion).

For a macro, that is a specialty lens that offers 1:1 magnification (image projected on the sensor/film is the same size as the subject). Typically, macro lenses have a flat focus field at maximum magnification (closest focus distance), almost no distortion, great sharpness, and the various aberrations are minimal. You would never be able to meet all these parameters in a zoom lens.

Because a fixed (non-zoom) lens produces the highest quality image with fewer compromises at the focal length.

Actually not all quality portrait lenses are primes. I use 50mm and 85mm lenses but I also use the 24-70mm f2.8 and the 70-200mm f2.8 for location portraiture.

They are not always fixed! You can, of course, use a zoom for portraits.
It's just that prime lenses are of slightly better quality and should produce a better result.

Because if they weren't then they'd be broken. Ohh I crack myself up!

As has been said they aren't all fixed. Technically they are telephoto lenses, but if they have a focal length of 85-135mm in whole or in part, then traditionally speaking they can be used for portraits. Fixed lenses within this range have been called portrait lenses because that's the primary use for the focal length.