they probably can't because some of the proxies were used by TLAs is my guess...

They worked on malware detection. The most likely reason is very obvious: if you only allow traffic from residential addresses to your Command & Control server, you make anti-malware research (which is most likely coming from either a datacenter or an office building) an awful lot harder - especially when you give non-residential IPs a different and harmless response instead of straight-up blocking them.