That's a very good point and even better pointed question!
Part of the value of the network is how much bandwidth one can use in a month. The other part is simply the convenience of being able to send/receive lots of data in short bursts.
I'd argue most people don't need to consume lots of data to appreciate 1 Gb connection when it's available. I think you'll find most people are willing to pay a premium for convenience and optionality, even when they don't use it.
Now, if they're not using more total bandwidth, then your point stands. If the network is idle, it's more than likely not to get built out at all, but I'm not sure that rule applies to last mile networks.
> I think you'll find most people are willing to pay a premium for convenience and optionality, even when they don't use it.
Not much of a premium. CenturyLink offers 1gbps in my area. I only know one person who's subscribed to that level of service. Cost has been cited as the deciding factor every time.
What will be taking the rest of the bandwidth? It certainly won't be idle or it won't get built out at all.