It’s very easy to chop your tyres up on gravel. Particularly on an event like Portugal, where the upper layers if gravel are rather soft. The gravel tends to clog up the treads, and when that happens, you need to be a little more judicious with the throttle. The problem is that the tyres clog up at different rates, and so you have to try and balance four tyres with different levels of grip. It’s a rookie mistake, but this is Kubica’s first event.
Also, he didn’t run out of tyres. If he had made it to the next service point, he could have put on a fresh set – but he ruined his tyres on the stages and ccouldn’t make it back.