the reasoning is two fold, from what i recall
1) a majority of the original staff here came from staff duties at 8bc at one point in time, and it was a big time-eater with all the name-change-requests they had there (i contributed to that work load, i must admit)
2) being that the forum is arranged to be tracked in chronological order, in order to avoid gaps or inconsistencies in the 'trail of knowledge' or whatever we would rather keep the names as they were in the conversation, and definitely don't delete stuff in order to avoid gaps. if we must, its moved to the graveyard to go and die (this was made to have an alternative to deletion)
some of the arrangements here are a reaction to what wasn't working at 8bc (from the staff's perspective there). if anyone remembers, information being deleted became an issue there so we started out with an approach to not let that happen here
i can recall only one name change here myself, but the circumstances were particularly unique (and staff wasn't in complete unison about that either). very unique circumstance.