Here's the thing.
By saying he will keep any licences already out there, he basically gave sunak the green light to do this.
Had he said 'I'll cancel all new licences if I win', then those new licences would have presented such a risk that they would be worthless, and no one would try to buy them at all, so Sunak would not be saying he will issue them.
Hell, even just saying nothing, something starmer is usually very good at, his best quality some might say, it would create enough commercial uncertainty to stop sunak doing this.
But no. He took the one option that guaranteed oil investors, such as the hedge funds backing him, and murdoch who invited starmer to his big party last month, would make a bit more money.