I would suggest that they are cleverly turning the screw.
And so entrenched are these attitudes, the leadership are actually incapable of responding without making things worse. Look at Diane Abbot's closing comments during yesterday's debate - backbenchers have called them a "disgrace". And Corbyn can't condemn one of his key allies, so that in turn turn cranks up the pressure on him
If backbenchers who want to force Corbyn out resign then they become powerless. Condemning him from within is far more effective.