Distributed bot and scraper networks. Thousands of IPs geographically dispersed throughout the world. There is only so much you can do with rate limiting.
Needing to be logged in as the same user defeats the purpose of proxying to hide your physical origin.
Registering thousands of different users to use in a distributed way is hard now that they require a text message verification for new accounts.
https://www.eff.org/deeplinks/2019/09/victory-ruling-hiq-v-l...
They were ordered to unblock hiQ specifically, they were not ordered to open up content to scrapers generally.
They can still throttle high volume traffic and put up captchas. I think the only specific thing the court ordered was for them to unblock hiQ IP ranges.