Which was nothing to do with Jeremy Corbyn or Diane Abbott.
Labour governments and parties of Attlee, Wilson, Callaghan, Smith and Blair were all heavily dependant on the Scottish and Welsh votes and the MPs they returned. Many famous labour figures like Aneurin Bevan and Jim Callaghan were Welsh. Even John Prescott with his fake northern accent is Welsh, born, raised and educated in Cardiff before moving in adulthood to Manchester. And Labour had also always relied on Scottish MPs, Blairs predecessor John Smith was a Scots MP, as was Blair's chancellor and successor Gordon Brown.
The disaster for Labour was devolution. Nationally the SNP were a small fish in a large pond, but with devolution that was reversed and the SNP soon swept into power in the Scottish Assembly and at Westminster by taking Labour's seats. These developments were with the Blairite Labour party of Blair and Brown, nothing to do with Corbyn, who only took over the party 8 years later.
At the time I posted in this forum that this fundamental change would make it very difficult for Labour ever to get in power again, since it left the Westminster constituency very heavily southern Tory biased. But there was worse to come in the form of the Scottish Independence vote. Many Scots who had swung to the SNP were strongly opposed to independence so they swung to the unionist party, the Tories, whose correct name is the Conservative and Unionist Party. That was even worse for Labour, not only losing most of their Scottish MPs but some now becoming Tories.
Yet Labour's bad news still wasn't over, since similar happened with the Welsh Assembly. The rise of Welsh nationalism and a similar backlash as in Scotland meant we have 12 MPs in Westminster who are Tory or Plaid Cymru rather than the Labour they largely had been before devolution.
So, as I've already posted to you several times, in this fundamentally Tory biased national position, Labour cannot get into power on its own merits, no matter who leads. Another Blair couldn't do it, he only won with the overwhelmingly Labour Scottish and Welsh votes which are mostly not there any more.
Labour can now only get there by the Tories failing, and that's what happened at the last General Election when May lost her majority. Her vote just didn't turn out sufficiently as a result of the Tory failings in government.
The Westminster electorate of the UK is now rather like that of the USA, either mildly right wing like the Democrats or very right wing like the Republicans. Here as there, true socialism has no place in enough electoral hearts to achieve power on it's own merits.
The selfish society wins for the foreseeable future.
.