We didn’t disclose it at the time but this 17.2M rps attack came from (home) Mikrotik devices that were running proxy services: https://blog.cloudflare.com/cloudflare-thwarts-17-2m-rps-ddo....
Still, if an ISP has had multiple abuse reports for the same subscriber and they're not doing anything, after some time it starts to become reasonable to block this IP, and in a further escalation, this ISP's ranges altogether until they clean their act up. I remember getting the Internet connection blocked as a teenager on an XS4ALL connection for being an ass on the Internet (I tried to DoS a domain squatter that tried to sell a domain I wanted for a thousand times the price with no added value). The abuse desk which I had to contact to unblock it took my promise to not do it again seriously (as did I), not sure how other ISPs handle this.