Why not? Because ISP don’t snitch on you in case of illegal streaming?

Correct. ISPs aren't monitoring for this stuff. They're responding to complaints they get from copyright owners. With torrents, anyone in downloading the file can see IPs for everyone they're downloading from. That's how companies get IPs to follow up on, and why VPNs protect you (they'd just the IP of a VPN server). They then compile lists of these IPs, send to ISPs, who are then compelled by the courts to send letters and eventually disconnect you if you get caught again.

With streaming sites, the only one seeing your IP is the host of the site. Of course they're not going to snitch, since you're just watching the illegal stream they've made available. They're the ones breaking the law in that case, you're just watching a public stream. Obviously, you're not expected to know whether every video on youtube was uploaded by the copyright owner. Instead, the onus for that falls on the uploader and host.

And what about usenet, I’ve read about it but I didn’t get it? Can you brief it out? How it similar to torrents and how it’s different?

Super high level: there's two external parts, an indexer and a usenet provider. The indexer indexes .nzb files that serve as references to file locations on the usernet provider. Practically speaking, it maps pretty closely to .torrent files and the actual content you're grabbing from peers, respectively. The important difference here is that the usenet providers host the content, rather than a bunch of random people (which can include corporate attorneys looking to contact your ISP).

Locally, you still use a client piece of software to download. You can send it a .nzb, and assuming it's configured correctly with your usenet provider(s), will download the content.

Other important differences: 1. usenet indexers and providers are going to cost money, unlike torrenting. They tend to be pretty reasonable if you're downloading a lot though. 2. Because the providers are more centralized than torrents, there's some quirks. Retention is a factor, and generally the older something is, the harder it'll be to find (or more expensive plan you'll need with your provider), and not all providers have everything (so heavier users may need multiple providers to cover all their needs). A single good provider covers like 99% of what I need though.