The fact that there is a heated debate about the efficiency in the roman numerical system speaks volumes about the people in this thread.
It's not exactly 'hard' to understand why VIII exists, sure it's not as efficient as possible, but does it really matter?
It probably came about in order, III isn't 'that' long, however IIII was ridiculous, hence why IV came along, VIII was probably to keep with that flow.
(Yes I am aware that III would be the same number of characters when converted to IIV, however the problem is with is in general with the subtraction later down the road, as subtracting 2 only requires 3 characters as opposed to adding 2).
LXXX, XXC for example.
It just happens, it's not like this is a widely used system in everyday life for most people, and it's not like it'll kill you type in one more letter.
What is this shit, xkcd?