is there evidence now that the coins are STOLEN (not lost or unavailable)? - for me it makes still absolutely no sense that a company can be abused by a thief on that scale.
There are lots of possibilities:
1. Mark sold the coins in 2011, to cover operational costs, assumin he could buy them back when everything was up and running, BTC price soared xxx%, he could not buy it back anymore.
2. He got hacked in ~2011 and lost the coins. No sane person has that many coins in hotwallet since 2013, back then it was plausible.
3. His coldstorage program messed up, and he lost the keys (I read some plausible theories on this on reddit).