I believe - as others have stated - that Labour's problems like with the powers that be, and their willingness to pursue a concept of what they think Labour ought to be, as evidenced in their manifesto, rather than what might get Labour elected, which is a very long way from that manifesto.
The Party, which elected and fully supports Jeremy Corbyn, and his version of the reasons for their loss, is obviously intent on electing someone who thinks the same way.
This willful need to ignore what the electorate has actually said, and why they have voted the way it has, speaks to the tunnel-visioned stubbornness of the elite, who seem more occupied with increasing the scope of their vision of socialism, and the need to offer policies which will attract enough voters to form a government, seems not to be an issue of any import at all.
As it stands, Labour are condemned to decades of irrelevance in British politics - it may take the retirement and demise of the current elite to occur before any new minds can actually engage with the notion of Parliament and genuine Opposition, and in the further future, Government, rather than sticking to their peculiarly cerebral notions of aims, which bear absolutely no relation to the real world in which their former supporters live.