Eyes are hard to do because of their complexity. They have a complex motion and a complex structure. This makes duplicating their aspect and motion hard to do in a "resource-friendly" manner.
Also, it might just not be that eyes are so badly done as compared to other stuff as it is more an issue of the fact that eyes are amongst the most studied parts of humans and what's around us. Maybe milk is not properlly done as well, heck, maybe it's worse than with eyes. Milk surface is tricky, there's lots and lots of sub-surface scattering and such. But since people tend to look more (and are more familiar with the aspect of) eyes than milk, it might just make so that eyes rendering is more criticized than milk rendering.
Also, at a supperficial glance, eyes seem easy. I mean they're just a shiny ball with some concentric cirles of various colors "painted" on, right :) ? This might lead the junior 3d artist into over-simplifying the task and making just that, a shiny ball with concentric textures that completly lacks, for example the subtle light sparkle that happends in every (living) eye.
Finally, eyes are small. Think XCOM Enemy Unknown (the 2012 version). 80% of the time you're in high-above-3rd-person view, you don't really see the eyes. But sometimes the camera zooms and changes angles so that you get a close-up portrait of the character. In such a setup (which is quite often), details which are not often seen from up-close (such as eyes) are intentionally left "un-detailed" so as to speed up development and conserve resources.