ISPs will gladly quarantine/rate limit folks for pirating stuff, why don't they use those tools to combat botnets? Though I could see this leading to a slippery slope of remote attestation for internet access.

> why don't they use those tools to combat botnets?

Because they probably don't care.

Where this breaks down is that because of the nature of the internet and DDoS attacks it’s not something that can easily be solved with better policing - even identifying a perp might be near-impossible, and they might be in another country anyways. The government does try to prosecute botnets and DDoS attacks today, but it’s of limited success. Is there a practical solution here I’m missing?

I don't know about a "practical solution", but there are research efforts to think about new ways to build internets that mitigate some of these problems.

Here is one that I'm aware of: https://named-data.net

Community yes. Government protection no. When was the last time you heard of police stopping a break-in or making a successful investigation ?

Independent of police, in bad communities your neighbors are willing to break in. In good communities they don't.