The Post Office is a good example for the Internet. Right around the holidays, everyone starts to send catalogs, Christmas cards, and other packages. Far more than the Post Office deals with on a normal basis. Which causes delays in delivery. They even warn people: send everything by such-and-such date or it won't arrive in time for Christmas.
That's pretty much the Internet. Everyone expects a certain amount of bandwidth to be used. Occasionally, someone will exceed that, but usually at the same time, someone else isn't using theirs, so it's okay. But with Torrent, it's basically everyone using their bandwidth all at the same time. It's always Christmas. Now, the Post Office could staff for that situation, but obviously, prices will have to go up to accommodate their extra load. Likewise, your ISP can provide all the bandwidth necessary to let everyone use their limit of bandwidth all the time, but they're going to have to raise the prices a lot in order to provide that.