Half Life 2 is only ~4-6gb and was designed to run on video cards with 128-512mb of RAM, and it didn't even do texture streaming so you just need to have those assets at load time. Sure you can stream those low res textures at an acceptable rate. That's wholly different from streaming the textures for a modern game, which are at least an order of magnitude larger, and are expecting to stream in from NVME/SSD storage.

This website is also a proof of concept, it doesn't care if people are actually able to play it consistently. It can afford to just say "anyone with less than 100mbps internet gets a shitty experience, lol don't care" and nobody will complain, because it's a free tech demo. Not an actual product trying to sell copies and make money. And certainly not anything remotely modern, we are talking about an over 20 year old game here. Technology did, in fact, get a little bit faster and more capable over those last 20 years, you know

Performance of the game is much more important than download time

Its really common to sacrifice disk space for runtime perf

For gamers 100GB is not a big deal, CoD is like 200GB and its extremely popular