As soon as you get infected or bring a kid back from college and let them torrent like crazy, the bandwidth overage costs get high, fast. I tried this for years with our customers, we're going unlimited because we're tired of arguing with people who can't comprehend this model.

What are the actual technical reasons, however?

Technical reasons? There are none. This is customer/sales driven, normal (non-technical and the majority) customers don't want to bother with technical bandwidth/transfer non-sense.

"Real" bandwidth that you're allowed to saturate costs an ISP about $1/Mbps/month, and that's not counting the cost of building the ISP's network itself which is probably much higher. Today's $50 broadband service is maybe backed by 1 Mbps of real bandwidth if you're lucky, but changing the advertising from "up to 15 Mbps" to "1 Mbps guaranteed" is commercial suicide.

Is this true of Google fiber? Probably not, and that's the whole point.

I would bet that almost all of the cost of Google Fiber is in the last mile; OTOH Google can probably buy bandwidth very cheap. It's probably still oversubscribed 100:1 or more.

> It's probably still oversubscribed 100:1 or more.

[citation needed]

If you want to believe that Google built a multi-terabit network that's 99% idle, go ahead.