He wasn't elected because they completely lost touch with there usual supporters in the old industrial towns over brexit and at the same time completely alienated themselves from the vast majority of the broad middle class with there socialist policies that were very much aimed towards 'the youth'.
I agree with a lot of your analysis, but for me it wasn't just Brexit!
It is true that as far as many of the 'red wall' voters were concerned Brexit was the 'straw that broke the back' of the relationship of these towns with Labour, but whilst Labour had been claiming for years to
represent the working population, it had stopped trying to do anything to
improve the lot of these towns many of whom had been ravaged; by decline of traditional industry, factory closures, loss of major employers, endemic unemployment, including de-skilling of the work force, and a host of moribund so called 'local initiatives' for years.
Many so called initiatives were short term funded at best and involved either going cap in hand to the EU for Project support finance, offered under grand sounding schemes, but often resulted in only the third or fourth level bid (
much reduced in value) being accepted; or Local authorities selling off traditional assets, to raise money or to try to attract new employers, e.g. lots of school playing fields sold off, landmark buildings went, devastation of many local habitats, e.g. when dredging was ended and rivers began to silt-up (
also later adding to flooding problems).
Many people still believe all this 'devastation' began under the Tories 'austerity' programmes', but in many Northern towns this had been happening for years. True, things did get worse in the last decade or so, but the rot had set in years before and even when it got the chance Labour did virtually nothing to halt the slide, and of course the Tories jumped onboard and continued the trend when they were in office.
Neither of the major parties even recognised there was a problem, until Brexit exploded in their faces, even then Labour under Corbyn ducked out and left the field clear for a 'levelling up' pledge from Boris. Of course its unlikely to happen because Boris has also pledged to go down the Carbon Neutral (Climate Change) path as well and the truth is he
cannot achieve both.... guess which one will get ditched!