There’s a strong fantasy among the left that governments can spend their way out of anything. You see that nonsense frequently on MN. Often I’ve seen posters say that countries can’t become bankrupt, since a nation can just print ever more money.
So I wouldn’t put it past the Labour left to stage or contribute to a coup against Starmer and Reeves - who are anyway a great deal more left in practice than their pre-election posturing would have had you believe.
Starmer’s problem is that he’s useless, wherever he is on the Labour spectrum. The left of Labour sees a chance, not an ideological enemy.