Cøbra is just upset by the political games running on the forum, some of his precious comments here clearly states that. It is one of the main reason he is not that active here I guess.
A lot of prominent members in the Bitcoin community started out on bitcointalk.org, then migrated to Reddit, and subsequently migrated from Reddit to Twitter. Many of these became "thought leaders" on Twitter, and no longer are active on Reddit or bitcointalk.org. I don't think it's because of the format or feel of the forum, I think it's more of an ego thing.
I somewhat agree with him on it as many prominent members of Bitcointalk have already left because of the same reason.
BTW, Cøbra is not a co-owner but the real owner of the forums domain and even the
bitcoin.org official website domain.