It's less about protecting them, and more not pushing away your customers. Very little activity on usenet isn't file sharing now a days and few of those files are above bar... But they'll take on that risk for you, for a little bit of your money. It's part of the business model.

Again copyright holders aren't generally interested in those downloading content, but those hosting the content to be downloaded. With usenet you are shifting that hosting away from you, and paying for that security of it being someone elses problem. If a usenet host gets taken down/raided, it's very very unlikely the authorities would then go after everyone on the customer list; that's neither practical nor worthwhile, especially as it typically crosses international borders amd very little info is stored about usenet customers. They'll just move on to targeting the next host.

With torrents, you are the host. You're broadcasting to trackers what content you have and the fact that you want someone to download it from you, painting a big target on your back.

Usenet also provides a little bit of reasonable doubt as the host isn't the one posting data to the service, and the files posted to usenet are broken into many parts and compressed individually. Without the index file (which isn't posted to usenet) to re-combine the parts in the right order and see the whole thing, it's not clear at all that it's illegal or copyrighted content to be able to take action on it. Maybe it was a rip of the new Guardians movie, maybe it's just a cat picture 🤷. This heavily delays the takedown process and allows the host to say they were reasonably unaware of the content, dodging responsibility/consequences.