'cause it's easy to divide into an even number of elements.
but then it's no harder to divide into an odd number either !
'cause you get a nice looking "fan" pattern of the elements ...
nothing suggests that the virtual world will come crashing down on you, invalidating your results, if you use an odd number of elements.
unless, of course, your customer has specified doing this ...
in which case the very real contract world will come avisiting your cubie.