Which is why they probably limit 'excessive use', and / or have hard GB caps in place, which basically every ISP does. If you paid for, say, 20GB of up/down traffic, and you can run your server within that, why should they be able to say you can't do that, just because it's a "server"? If you had uploaded 20GB to e.g. Dropbox, they aren't complaining.
If you have Google's fiber, even if they say it's unlimited, they still have the ability to restrict your up/down speed (I'm assuming, given the legal support of all the past "unlimited X!" that sometimes gets throttled to extinction). Why don't they just limit it if you're being excessive, regardless of the purpose? Or offer extended GB/TB packages and put hard limits somewhere?