I am not sure what you are trying to argue here.
Are you saying the left has not been affected by the failure in their attempts to create an effective non-capitalist society?
There is no one in politics today trying to create a true non-capitalist system. There aren't even many attempts to try and outline theoretically what that might look like, and none to try and implement it, or with any practical sense of how to implement it.
Even the Communist parties are not talking about anything like that.
Right now global capitalism is the only thing going, and all the political parties are working within that. The only partial exceptions might be North Korea or Iran, and I don't mean they are authoritarian, I am talking about economics. And their economies are shit.
This is a major reason that it doesn't really matter which party gets in, there isn't much chance of a really different approach - they are all heavily constrained by an economic environment they don't have any control over. The market will accept certain things, and that's that.
If people who think of themselves as on the left have to square that with accepting global capitalism, what does it mean to be on the left?