I think they were making a show to try and put Starmer in a hard position, and find some sway over party positions through it. Only Starmer has no interest in stunts and wants to get on with the job in hand, so considered it to be better to let them go than be seen as weak by being swayed through rebellion. Like you say, Starmer’s Labour has stressed that there will be hard decisions due to financial constraints, but this benefit constraint better go in the end.
