I think that comes back to the belief that any success is by definition evidence of privilege - since it is privilege to be able to succeed- and so any success is intrinsically unfair. They believe that - morally - the fruits of that success should be shared amongst everyone - with as little as possible given to the person who caused the success.
That seems to genuinely be their world view- and that of many of the pro-Labour posters on here.as well.
It's the most extreme form of socialism - and to us it's obvious how damaging and wrong it is, with our belief in the importance of personal responsibility and the moral justice of getting out of life what you put in.
But as I see similar happening in other Western countries - notably France - I do wonder whether this is the inevitable trajectory of our current social model with it's ever-increasing welfare state, and will lead to it's end.
As in the Alexander Fraser Tytler quote about voters discovering "that they can vote themselves largesse from the public treasury. From that moment on, the majority always votes for the candidates promising the most benefits from the public treasury with the result that a democracy always collapses over loose fiscal policy, always followed by a dictatorship."
Hopefully we'll just have a swing to the right as people realise how unsustainable it is - but the longer it goes on, the stronger the swing will be. The welfare state has existed for less than 100 years: we all like having it (but not paying for it), but it's far from a core and necessary part of society and perhaps - like communism - it simply doesn't work as a model.