Zarah Sultana and The People's Front of Judea

Zarah Sultana has stated that she and Jeremy Corbyn are to create a new left wing party.  What I want to know is why.  We already have left wing alternatives to Labour, Plaid Cymru in Wales, the Scottish National Party in Scotland, in Northern Ireland we have Sinn Féin and the Social Democratic and Labour Party while nationally we have the Green Party and the Liberal Democrats.  We also have the Workers Party of Britain (with George Galloway at its head) and the Socialist Workers Party (which did not stand at the last General Election).  Most in England who are to the left of centre, but do not wish to vote Labour, decide to vote Green or Lib Dem.  The Greens are felt to be more left wing than Labour, and the Liberal Democrats are more left wing in some areas, and not as much in others.    

So when someone wants to create a new party, I want to know if it is a good idea for them to take left-wing anti-Labour votes away from The Green Party.