I'm not sure why it's a surprise there are ex-Labour voters.
The whole point about Nu Labour is that it moved significantly to the right to capture voters there.
It actually became a cliché that you couldn't get a cigarette paper between the policies of Nu Labour and the Tory party.
There was little effective opposition in Parliament to many Nu Labour moves because they were what the Tories wanted anyway. The privatisation of the NHS was something Mrs Thatcher didn't dare do, but Nu Labour were working towards it when the Coalition came in and finished the job (though perhaps not exactly as Nu Lab planned, but hey, they skinned it, the Coalition cooked it).
There were many effects of the Nu Labour government, many of them good, eg national minimum wage. But among the less good ones are that it moved the whole dialogue, the Overton Window to the right, and that it left people who eg didn't want the NHS privatised with no one to vote for and no voice in Parliament.
Now that Labour is moving back to the left, it's entirely natural that it should lose those same Nu Labour voters.
For this coming election, anyone who wants Tory policies will vote Tory. Anyone who doesn't want Tory policies won't vote Nu Lab. So Nu Lab doesn't really have a function any more.
There IS a function for a working opposition to hold May to account in Parliament and voice ideas the Tories certainly won't. But infuriatingly we don't have that, because Labour hasn't finished ripping itself in two and Nu Lab sailing off to form a centrist party with what's left of the Lib Dems.
A Labour government which simply enacted what the noughties Tories would have done anyway, and in particular which continued harming the most vulnerable and leave "ordinary working people" unable to afford accommodation or childcare... I'm struggling to see the value of that.
By the way, I'm disabled and unable to work. I'm supposed to be doing my DLA/PIP renewal today, not writing this. I didn't have well-off parents but am lucky enough that my own generation (inc white van bro) are still able to work and have promised to look after me when the benefits fail - as they already have a couple of times. Dependence is not a nice position for an adult to be in, but I appreciate I'm extremely lucky to have people to be dependent on.