I suspect incentives play a huge role here. OAI employees are compensated with stock in the for-profit arm of the company. It's obvious that the board's actions put the value of that stock in extreme jeopardy (which, given the corporate structure, is theoretically completely fine! the whole point of the corporate structure is that the nonprofit board has the power to say "yikes, we've developed an unsafe superintelligence, burn down the building and destroy the company now").
I think it's natural for employees to be extremely angry with a board decision that probably cost them >$1M each.