To a point, some people are going to vote for Labour whoever the leader to get the leader
However Labour have moved more central under SKS which is appealing to a lot more people - reform NHS/more defence spending/getting people back to work/stop the boats etc etc - people are wanting this, so...
He is the Left version of Reform.
Labour are looking more electable the closer we get to the election with policies such as reforming the NHS, not just throwing money at it etc etc
A nice move from being elected just because they are not the Tories.