They want Labour to go back to where it was heading before the 2015 leadership vote-to the RIGHT of Tony Blair.
These were the people who wanted the party to endorse the benefits cap and the budget charter, while keeping Thatcher's anti-worker laws in place.
Can you not see that if Labour did those things, it could never do anything compassionate or pro-worker or pro-human decency again once in office? That those policies would commit Labour to the permanent austerity policies that have made every social democratic party on the European mainland unelectable? The policies that turned all of those parties into enemies of the labour movement in their countries?
That's why McCluskey would have no patience with his deputy doing these things. He was wrong to suspend the guy, but would you really expect McCluskey to be cool with him giving aid and comfort to people with no positive intent, people whose only motivation is to make Labour indistinguishable from the Tories on all major issues?
Ask yourself this...if Liz Kendall had won the leadership, could you think of any good reason for any union in the UK, or anyone there who cared about progressive change of any sort, to even bother to work to try to elect a Labour government with her as the leader? This matters because Kendall is the person most of the PLP wanted as leader.