"How can the ISPs claim to be "affected" by excess traffic when they charge for bandwidth already ?"
ok will try to explain this part. there is bandwidth allocated for specific use. Now, the amount of usage can exceed the amount of planned bandwidth... this is like trucks being overloaded messing up the roads, or tables in restaurants occupied by one guy, or flights being overbooked, or concert and theater tickets that have black markets. All of this happens in the digital environment. There is so much you have planned for, and so much use that occurs.
now these things use bandwidth continuously. it's more or less like the device is constantly sending things back and forth to the internet. at some point it stops making economic sense for air to carry this kinds of signals. this is a kind of pollution. we are not at a flash point yet, doing some quick calculation europe has 8 zeroes in it's population, we have 9. 10% of us is the same order of magnitude as them. their penetration is above 100% so that put's them in the same ballpark as us.
your phone line can charge you your cable bill. not done yet. that's sent over the air. that is the problem. there is not enough airspace for all these things. It's ISPs saying early on that they will not be able to viably support this kind of usage.