Seasend
CarboCookie
Seasend
OtakuKat
Did they even say why they were retiring MG and HoC?
It's likely because of a low playerbase and costs to keep the servers running.
Most likely this, plus I heard something about them having trouble with Viximo servers which hosted MoGa (along with Resort World and Backyard Monsters).
Never really played Moga before, was the idea and game owned by gaia or "rented" from another company?
No, no, Gaia made Moga, it was their idea. It's just that it was originally designed to be exclusively for Facebook, but of course no one liked that for obvious reasons, so they moved Moga to Viximo servers. Viximo is a company that provides servers for 3rd party gaming websites that don't have enough infrastructure to host the games themselves (like Gaia, presumably).
I guessing (not sure though, they've been very tight-lipped about everything), that they had a contract with Viximo and possibly Facebook preventing them from moving to another server, and due to a lack of interest in both games (due to bugs, loading times, low gold-earning potential etc.) that they've decided it's easier and cheaper just to abandon the projects.
But that's just a guess at best, whatever the reason however, it's totally lame.