The cable coming from the street to my home is RG-6. There is some disagreement between different things I've found Googling as to the maximum data rate RG-6 can handle, but it seems to not be over 1.5 Gbps.
That would put an upper limit of a little under 500 TB on how much data it could handle in a month.
The cable going from the equipment on the pole that my cable is connected to doesn't look to be any different. I can't get a good look at it to tell what it actually is.
Looking around my neighborhood and surrounding neighborhoods that's all I see. I don't see anything different connecting my area to whatever is upstream of all of us.
That suggests that a whole bunch of us as a group have a physical limit of 500 TB internet data per month. (Actually less because those cables are also carrying cable TV).
Obviously they can't serve a whole large city or region on just 500 TB aggregate data per month, so they must have something with higher capacity going out to some kind of nodes that split out into multiple connections to the lower capacity part of the network, probably a multiple level tree topology with decreasing node capacity the farther you get from the root, but I've not been able to actually find any of those nodes.
Presumably when they need more than 500 TB per month for some area they have to replace the top node in that area with a node with a higher capacity connection to its parent, and then have that node serve two or more 500 TB per month nodes. How easy or hard and how cheap or expensive that will be likely varies a lot from neighborhood to neighborhood.