Because those running the show right now is the economic majority which means big market makers, those who sell the biggest amount of coins to the public. If they do a move, miners will follow, there is no doubt about that but these guys are being cautious and therefore slow to move. A bunch of them have settle December as a dead line back in August and now, as we approach this deadline and as the block are being full and the economic pressure is building up, Coinbase (which have received the largest investment) is now stepping up stating they will lead the move keeping the same date. It will happen, one must get prepared.
How much of Coinbase's liquid assets are actually
in bitcoins? If I had to guess, I'd imagine them to be a company which functions fully on fiat besides their operational requirements.
I suppose Gemini, with the information I have (twins own a lot of coin), is actually part of the economic majority, but I'm not so sure about other "Bitcoin" companies. It would be interesting to know how many of them are actually part of the economic majority.