The main draw is the free BT Sport which I wouldn't have paid for but being it offered free is a good reason to switch when everything else is equal ....
If you take Sky broadband and phone line, which is much cheaper than the equivalent service from BT, then even though BT throws in BT Sport free, Sky works out cheaper by £4 pm.
BT phone & broadband per month plus free BT Sport = £38.00
Sky phone = ................£14,50
Sky broadband =............ £7,50
Sky cost of BT Sport........£12,00
_____
Sky Total per month = £34.00