This is the cost of how much bandwidth uBO
currently incurs on
each server freely hosting the filter lists -- keep in mind these lists are updated every few days. The lists are currently freely hosted on a couple of servers, each of those servers see the kind of bandwidth shown above if not more. And notice that the price tag above is only for North America.
If we let this sort of bandwidth usage grow unbound, it's not going to be free anymore, and you can see the sort of cost we would face -- it's essentially an end to the project.
Version 1.54.0 of uBO will support
differential updates, this should significantly reduce bandwidth while having lists update more often.