From that article : "A trial of a ‘yellow card’ early warning system helped hundreds avoid a loss of benefits – but the Government has not agreed to extending it across the country"
They say they need more evidence. What more evidence do they need? Extend it across the country and monitor how it goes!
Even if someone "deserves" to lose benefit, it's only reasonable to warn them that it is going to happen, not just snatch it away unexpectedly.
Under the current system, even people who have never been sanctioned, and who have complied with everything asked of them by the DWP, must be terrified that it could happen to them, completely without warning.