actually, why couldn't the ISPs just give the ppl an uncapped 10MB/s(or whatever their fastest lines are) line and bill them $/GB?
Because data is not the limited resource, bandwidth is. You do not "use up" GB, like you would energy or water.
Compare internet connection with, say, water or natural gas (I pay for every m^3 used). Once I used that water or gas, it's not coming back, nobody else can use it. If nobody uses it for a while, the amount gets saved and can be used later. The pipe size does not cost a lot, you can have a big pipe if you are planning to use a lot.
On the other hand, the gigabytes are not limited and they cannot be "saved". If nobody uses the internet for an hour, there is no more resources for the future - if you have a 10mbps network and you use it only 1 hour per day, you can't get 100mbps ("save up" the gigabytes for the time you need them), you are still limited to the bandwidth. Same thing on an ISP scale. The bandwidth is limited, but if the devices are idle (nobody is sending anything) they do not consume less power or wear out slower. The maintenance costs are the same whether the device is idle or fully utilized. Because of this, ISPs overbook the connections (sell 10mbps to 100 people even though they have 100mbps network for example). However, if all clients use the connection at the same time, they cannot get what is promised. So, one way ISPs decided to limit this was to limit the amount of data you can transfer, but this, in my opinion, is dishonest:
1.As I said, you cannot save up data, so if everyone decides to watch online videos at the same time, you have the same problem.
2.Limiting the amount of data you can transfer is just another bandwidth limit (100GB/month is ~300kbps and they want me to believe I am getting 10mbps?).
3.Since the limited resource is bandwidth, people should pay for it.
4.A lot of transferred data is not what the people want, for example, ads, spam. There is no equivalent for water, gas or energy.
Some ISPs play the "40% of bandwidth is used by 1% of clients" card - well, in that case either upgrade your infrastructure or do not offer such high speeds. Yes, a lot of people do not use the net for downloading, just for emails and such, but the ISP wants more money, so the slowest connection is usually 5mbps or so, so those people have to pay for it instead of the 1mbps they would be OK with, so of course only a small percentage would actually use what they buy.
Usage time in dial-up days made sense too, PSTN is circuit switched, so whether you are using the connection or not, as long as the call is on, the channel and the modem at the ISP is used and cannot service another client. A always-on (DSL, FTTH) connection uses dedicated end-point hardware, so even when I am not sending anything (or maybe not even connected), the DSLAM port cannot service another client.
