Bandwidth certainly is a scarce resource as is the equipment needed to support it. Fiber doesn't just magically appear in the ground. Switches don't grow on your street corner. These things have to be paid for and maintained. It only makes sense that the highest users pay for more for the infrastructure. It's the current pricing schemes that I have a problem with.

Typically it is not. It's not unlimited, but a scarce resource is one of which there is simply not enough to go around.

With cable modem pooling it can approach scarce resource status, but typically your modem does not "run out of bandwidth".

That's the throughput, though (which was always capped, in Mbps) not the amount of data. The latter is unlimited.

They're limiting the amount of data not because it's scarce, but because that forces people to limit their throughput - since if you use at the max levels, it'd reach the data caps in no time - because they're overselling too much and don't want to pay for the infrastructure upgrade.