How many people would stand in front of their boss and the rest of the world and say that they don't support him? That's what this open letter is equivalent to.
You may want to double check that. Their letter was in support of the CEO from 3 days ago. Although you’re right they don’t support the new CEO appointed within the last 24 hrs, but they don’t explicitly mention that, but they do lambast the current board of directors — and I imagine the the board should feel embarrassed, but save one, there’s no evidence of that.