JC was popular amongst Labour rank and file. He was a socialist and had always been one. He was pure to his beliefs and a genuine person (for a politician). Moving to floating voters the majority don't really want a socialist (who had a history of being a bit radical and a whiff of a mature student protester). It better for Labour to have a serious, bordering on boring person in a dark suit with a female deputy who doesn't say they want radical change - Blair and Brown did it in 1997, 2001 and 2005. I feel Blair needed to do more for the less well off in this country and not get involved in invasions of other countries. There is a gap to appeal to those in left behind areas of the UK, but Labour were not interested enough as the Conservatives in gaining those areas. Labour already had most of the English big cities, but they needed the working class areas away from a large city and they needed the Welsh and Scots to return back to them, particularly the Scots. It will be interesting to see if promised major infrastructure projects in the North materialise over the next 5 years.
I feel the Conservatives have gone as far as they can to the Left without losing their creditability as a right wing party, like Blair did with Labour but the other way round. Labour to me needs to endorse Brexit (instead of fighting it), put in special measures for economically deprived areas of the North and other similar areas of the UK. They existed in the 1970s but have withered away since, because investment has been too concentred in major city hubs, particularly London and people were in general expected to move or commute to these major city areas for professional work. The idea was that the wealth generated in say London would trickle down to other areas of the UK. Manufacturing (with a few high profile exceptions) was relatively neglected as it was thought we could buy in everything we needed from countries such as China at lower cost, with money earned from services, particularly financial services. Some of this was not talked about in public but it was clear from Government actions and inactions (both Labour and Conservative). A start would be incentives to keep young professionals/graduates in economically disadvantaged areas (say through payment back of tuition fees), tax advantages to businesses and individuals in certain geographical areas, internet infrastructure to a very high level, movement of Government departments out of the South East and Metropolitan areas, restoration of local HMRC offices, more support for manufacturing operations opposed to services say through removal of government policies that has increased the price of energy, maintenance of a competitive exchange rate. I am sure there are lots more if people were asked.
Endorsing Brexit does not mean not working with the rest of Europe, but developing a model that works in Norway and Switzerland with some limitations on immigration. If Labour politicians keep going on EU marches they are not endorsing Brexit.