I asked this same question once before and it boils down to there's really no way to delete people who aren't active unless someone wants to go through every profile and delete those who obviously aren't here anymore. I suspect that will never happen for a variety of reasons.
My suggestion was to add a box in the member search area that you could refine the search based on the last time someone was active but so far I haven't seen anything of the sort.
Long story short, there's very few people actually running this site and they probably have better shit to do
