Back when I managed teams that dealt with API traffic at a unicorn, this wasn't the case. We'd ban a /32 and several times customers would start reaching out to our support portal (which ran behind different ingress rules) asking why they couldn't use the site a couple weeks later.

I've never worked on the ISP side so there's no doubt that there is a process at the competent ones, but my guess is most users do not have a competent one.