I imagine Facebook want the CR traffic and can monitor us all the more, to send even more adverts at us. Perhaps more seriously the move to mobile in photography is a key driver with its immediacy. As an apple aperture user its front and centre of forcing workflow changes on me. Is that really progress, it may be....
My issue is I still don't see mobile as a serious solution to photography. Snaps yes and sharing, but would I really get up early to catch a beautiful sunrise with just a leading mobile camera, no.
Using desktop mode allows me to be able to filter the adds, why sign that right away with Facebook, hopefully enough of you are happy being served adds so the site remains free and profitable for CR and I can enjoy the rumours with minimal distractions of pension planning or China brides, biker babes mentioned earlier might be a good change.