Smooth Extra is available for areas which do not have the proper Smooth Radio station on local FM/MW/DAB. They can't make the main Smooth station national because some of the local stations are owned by Communicorp rather than Global.
As for why they've added it to Sky, that's anyone's guess but they're paying for it so they can do whatever they like.
Quote:
“ i would not let global to add their smooth extra on sky channel 0146 at all i would have got this radio station the wireless from age uk on to sky channel 0146 or decades radio”
Both of those radio stations are probably more than welcome to go on Sky if they're going to pay for it like everyone else does. I shouldn't think Sky care too much what's on there as long as they're getting paid & everything is within the rules.