"sell their souls" ?

Steve I'm genuinely shocked by your attitude mate.

That's not selling your soul, that's doing everything you can to develop and polish your birth talent to make the best music you possibly can that you can be proud of and that (some) other people will love. In other words what every artist (and collector or interpreter) from any genre has always done.

Selling your soul is compromising your beliefs and values for the sake of financial gain. I can assure you Rachel and Becky are doing nothing of the sort. They have taken something they love doing (and have grown extremely good at), which is singing dark and interesting songs, simply and effectively - using deliberate understatement (both for effect and because it suits their voices) employing fully traditionally-informed vocal styling, and then, with Adrian's help, achieving a real frisson by setting that pale watercolour into an expansive but still understated frame of moulded gold - like a watercolour by Turner.

People like them because they think it's a simply brilliant thing to do, and to many it's starkly beautiful. Not everyone agrees - and that's fine too.

Is it anything to do with folk? Who cares? Do they expect everyone to like it? Certainly not. Is it selling out? Well if it is then so is everything you or I have ever done, mate.