I don't quite understand your post, but is your question why don't the ISPs of the sources of the abusive traffic sort it out?

The distributed nature of DDoS means each participating host isn't sending that much traffic, and there are often tens or hundreds of thousands of participating hosts. An ISP should verify claims of abuse before cutting off customers, and since most of the customers are presumably unaware of what their systems are doing, there will be a lot of unhappy customers and then you've got to spend a lot of customer support time on helping them clean up their systems so they can get back online.

I spent a fair amount of time sending out abuse reports for phishing / malware senders about a decade ago, and most abuse reporting addresses are a black hole. Even if you do get to someone who will do something about abuse, they won't do it quickly.

There's be a few high profile longer term DDoS attacks lately, but when I was running infra that got a lot of stuff, it was mostly people kicking the tires on DDoS as a service offerings and most attacks were 90 seconds long ... there's no way I'm convincing an ISP to drop a pwned customer over that.

Starting from there, this DDoS sounds like layer 7 DDoS which is easy to track to the immediate senders, but a ton of DDoS is volumetric stuff, often volumetric reflection attacks where the senders spoof your address. If you're getting that, best you can do is get the reflectors kicked off (or cleaned up) ... tracing back to the sending hosts means getting a reflector (and their ISPs) engaged to do a lot of labor intensive work.

All of that investigation stuff takes qualified people lots of time, that's your money reason it doesn't happen.

> most attacks were 90 seconds long ... there's no way I'm convincing an ISP to drop a pwned customer over that.

Every victim (such as readthedocs), or even people sharing blocklists to avoid becoming a victim, blocking that ISP's ranges until they do clean up their network could be a convincing argument?

As you say, even at 90 seconds, it's clear to all involved parties that the customer is pwned or malicious. Such a reoccurring source of abuse needs to either clean up or find themselves a different ISP to spread harm onto the net

I get what you're saying about that this won't solve an ongoing attack right this minute, or even by next week. But if we just let it all happen then the solution is going to be either (1) we all buy equipment that can handle something like a terabit per second and arm our infrastructure to the teeth or (2) centralize all traffic through a vetting entity who decides which client gets to visit the internet today. So far we're headed towards the latter and nobody really wants that. Abuse messages will have to slowly trickle down from victims to originating ISPs to users, and if users didn't willingly sign up, then to wherever users are getting this malware (Google's app store will be a big component). Stopping this at the source seems to me a much more desirable long-term solution