I think it's important to clarify what you expect of a witness. Some expect them to develop the core protocol further. Others just to produce blocks and add value in other ways. In the past, it was difficult to develop the protocol because Steemit, inc controlled the Github repo and was already paying developers for code updates they thought were important (not necessarily updates the community valued). Witnesses trying to build SMTs or MIRA or Communities while Steemit was working on them does not make sense. Now, with Hive, there is no Steemit, inc so the community (including the witnesses) can move forward on their own. Staying on a centrally controlled blockchain seems like an odd choice to me since a blockchain is supposed to be decentralized. If one person can control everything, what use a blockchain?