The Left wins because it has taken good lessons from religions.
 
It does not throw people under the bus for moral failings if they're effective (and as it begins to purity spiral more and more it hurts itself).
 
This is no more evident than when watching Conservatives cry about Leftists hypocrisy. The Left certainly doesnt care about hypocrisy. They'd argue failing to meet standards is irrelevant for them
 
They also offer absolution. Becoming a leftist, especially an effective one, white washes you of your past sins. Even of you lived a life antithetical to their ideals.
 
This is no more evident to me when watching moderate leftists or commies cry about DNC corruption or cronyism. That engine is why they win. It just failed because of a weird year, you would have fallen to 2016 too.
 
And as they fail to do this more and more by constructing a 'church with no salvation' their power wanes.
 
Right wing movements, from Buckley to White Nationalism, fail because they purge and disavow and infight and purity spiral. And no, purity spiraling is not a buzzword. It's a legitimate term to describe the one-ups-manship and infighting which spells the death of whatever movement has it.
 
Religions also weaken when schisming.