It looks like this is the reason: https://github.com/steemit/steem/pull/936
Dan wanted to open licence of Steem (anyone could then fork Steem without a permission of Steemit Inc.) - that would allow test many assumptions much faster, like every other altcoin is testing new approaches for bitcoin. Unfortunately other guys in Steemit Inc. do not share vision of Dan.
RE: Today I submitted my Resignation to Steemit, inc