I too was a giant fan of Akio's Mansion. His site and his stories (Emi-Chan) were what introduced me to BE and then later this Archive. Akio inspired me to start writing and reading BE stories.
I did some investigating a while back on this subject. His old, original site is still up (the one he had before he moved to the BEA), but the e-mail address no longer works.
From what little I knew of Akio, I got the impressiong that he was pretty young, problaby late teens and then early twenties when he was here at the Archive. His writing style suggested this, and I seem to remember hearing him speak of creating many of his first drawings on notebook paper during "class", which would ~definately~ pin him at around the 17-22 age range.
Knowing all this, my best guess is that he pulled his site away after somebody important in his life found out about it, either his parents or another concerned loved one (like a girlfriend or something). Akio was never as "hardcore" as the other site owners here. I think he was mostly maintaining his site out of a mixed-up love of anime and his still-young (perhaps unmatured) hormones.
In getting older, perhaps he realized that this genre or industry or community (or whatever you want to call it) was not something he wanted to be associated with.
I say this because I think I am very nearly the same age as he, and this is a very, VERY serious subject that I have had to consider as I've grown older and noticed with a more judging eye the community I've chosen to "hang around". I mean, I've all but quit all of my once daily "archive activities" except just to drop in every now and then to see how things are going. I can see where a person like Akio, if he was not forced out of it from an outside source, might pull his site out of a pure conscience issue.
Kay-sara...