It's one thing to promise these things, but another to be able to implement them. Why do you think they've not been implemented up to now? Is it because the politicians who've been in charge of the government are dishonest or incompetent or not determined enough? Or could it be that capitalism cannot be reformed into a "fairer" system?
Why are pensions, benefits, etc under threat? Is it because the politicians are bastards who want to make things worse for people? Or is it because improvements in these would have to be paid for out of taxes on profits which, since profit-seeking and profit-making are what makes the wheels of capitalism go round, would risk provoking an economic crisis if implemented?
Why did the Labour Party which set out to gradually change capitalism gradually change into an alternative management team for Great Britain PLC? Could be because governments can't make capitalism into a fairer society even though they might want to? And that any party which takes on the responsibility of governing capitalism -- which Plaid or the Greens would have to do to implement their programme -- has no alternative but to govern on capitalism's terms and give priority to profit-making over all other considerations?