This resurgence is largely because the centre-left is looking for a way to make welfare popular again. And contribution is back in favour because of something I think we can call the 'paradox of public opinion'.
The paradox starts with the perception that many people don't like aspects of the welfare system. In particular, they don't really like out-of-work benefits and - increasingly - certain universal payments. Over several decades, and increasingly so at the moment, politicians (especially the Conservatives and the Liberal Democrats) have interpreted this as a public demand for greater means-testing. To focus the system on those who need support the most. Subsequently, as 'demand' has risen for means-testing, the use of it has gone up in the benefits system.
However, for those on the centre-left, the greater use of means-testing reveals a difficult paradox in public opinion. This is that although the way to placate public distaste with the welfare state appears to be to respond to it by means-testing, such a response ends up creating a vicious circle. One where the feeding of public 'hunger' for welfare cuts only creates a larger appetite.
For many on the left, reasserting the contributory principle offers a hope of reasserting support for the welfare state. This is because means-testing concentrates social security on an ever decreasing group of people, meaning that the vital ingredients of public support for welfare are lost: self-interest and solidarity. Contribution could - the argument goes - revitalise both ingredients: by widening the pool of people who benefit from the welfare state and by making welfare more reciprocal.