Likewise, if 3 family members have it, and another one is thinking about joining Sky but thinks it's too expensive, then for only $25 they might change their mind. Hence, Sky gets more revenue.
The only down side is when the Sky technician shows up to do the install you have to get all the boxes back to the same address for the one day....
https://www.youtube.com/watch?v=IUB-wjXUREE