She's a great young musician with enormous success and following, which naturally leads to endorsement from the advertisers. It's very plain. And while her fashion may not appeal to everyone, it sets her apart - although one would argue she would generally be a more suitable fit for the brand of i-D, but currently the distinction between various fashion magazines barely exists so here we are.
I think those are horrid covers. Her McDean(?) cover from some years back was that much more interesting, if only based on the fact that she was styled so differently to her usual dressing - and I think that's what fashion magazines are for when it comes to celebrity.