I'm only a small-scale sysadmin but the way that I understand the internet is that you send abuse notifications to the IP address block owner and, if it doesn't get resolved, you block. The whois/rdap database reveals which IPs all belong to the same hosting provider or ISP, so you can summarize that all to one list of IP addrs + timestamps per some time period

The ISP actually knows which subscriber is on that line, can send them notices, block them, terminate them... loads of things that you simply cannot do because you have no relation to this person. And frankly I wouldn't want to need to have a personal relation with every website that I visit; my ISP can reach me if there is anything relevant to continued use of the internet. From personal experience, when I was a teenager, the ISP cutting our household off after an abuse report was an effective way of stopping what I was doing