You're assuming that an uncapped service
is viable to offer. In many areas, it is. In many areas, it is
not.
It is viable for mobile services, even though I think mobile
operators have taken the model a little too far.
But for fixed line services, it is mainly used to print free money,
or limit investment in the network. I'm okay with either model an
operator chooses to take, because until someone else comes along to
break capped services on fixed line, there isn't much anyone can do
about it.