2 - quick answer - If they're not done right your guys all look like loons, long answer - fully painted eyes bring a level of complexity and detail to the model which isn't required for standard tabletop paint schemes and if done incorrectly can look awkward.
3 - Its just not included in our package at that level.
I know that may be cold or crass, but it is true. I wont even claim to be that good at doing eyes. Jirhon, our other artist is great at them, i usually sub out any eyes to him in fact as he likes doing them and he is good at them.
Now as for tutorials I will point you away from myself and towards some people who are better then explaining things than I.
basic eyes
reaper minis tutorial: here
ultra detailed eyes
Destroyer minis tutorial: here