That is starting to get out of the range of what is easily available. 10Gbps circuits are commodities (I had one at my desk at my last job), but 100Gbps circuits are still pretty pricey. And, it's not necessarily trivial to get that kind of throughput on file serving out of the box; this bandwidth is something like CPU <-> video card, not disk <-> cpu, or cpu <-> network. Some tweaking is for sure going to be necessary if you are self-hosting this, and now you're tweaking network parameters and writing a custom file server instead of writing your game.
The cloud here is making something possible that should never have been possible, which is pretty cool. Being able to go from 0 infrastructure to 30Gbps of file serving without lifting a finger is somewhat impressive... but with that fast iteration times, comes the entity that did all the work wanting their cut. It seems fair to me, though perhaps not economically viable. Such is life.
Wait... you mean the actual computation is running client in the browser? I didn't even open this "game", but I assumed such high cost is because there is a separate GPT-2 running on a GPUs for each and every user.
This is what makes the price so surprising - you are copying data from one Google Service to another, but it's billed as egress.
Like I said before, this is one of those things that wouldn't exist without the Cloud. If you run things on your user's computers, you have to send them a lot of bits. If you run things on your own computers, you're spared that bandwidth, but now have to have enough "computers" to satisfy your users. It's simply something that's not super cheap to run these days.
I will admit that it is surprising that Google <-> Google traffic is billed at the normal egress rates, but the reasoning does make sense -- a 30Gbps flow is nothing to sneeze at. That is using some tangible resources.
The larger problem is that people didn't actually download the model, but apparently got custom server instances that got a copy of the model plus a gpu to run them on.