I played on v2 of Legacy and left before the 2nd wipe. Over the last several months I've somewhat followed the forums there, and it seems that Itakou just got bored of being a GM. Some players seemed to think it's because there were criticisms of his GMing, and they believe he retired because he was tired of that criticism. He didn't say anything about that, though.
If I had to guess, I'd say he got tired of Legacy's reputation. On the other servers I've played on, Legacy had a reputation for being something of a joke after v2. The donations became controversial, the sheer number of wipes were constantly mocked... one wipe was apparently caused by a security breach using Itakou's own login/pw information to create and distribute items. On other servers, people who still played on Legacy were considered silly or stupid for staying on a server that was guaranteed to wipe about every 4 months or so.
Itakou also seems to have a detached and grandiose attitude towards everything. He often claims that he had the biggest private server ever in existence, and that it is an incredible accomplishment (or something to that effect). Apparently, he believes this makes up for the constant wipes and other problems.
I'm not really sure, but I heard a rumor that he is anonymously starting a lowrate, as the head GM, under a different name. I'm not sure if the rumor is true, though.