What if Google and Cloudflare collectively reverse-DoSed all the infected IPs, not by sending them any traffic, but simply by refusing to accept any connections from them to any part of their infrastructure?
Whoever is on those IPs will suddenly find that half the internet doesn't work anymore. Which is probably a good enough incentive for them to replace their router, format their PC, or whatever else is necessary to disinfect themselves.
In many parts of the world, landline IP allocations tend to be stable enough for this to have a real effect. Phones are a different story, but phones are also much less likely to be useful in a DDoS botnet. (The owner would immediately notice the sudden heat and data usage.)
If we're going to live in a world where a small number of companies own half the internet, at least they could use their power to do some good.