Why doesn't Yahoo block the IP address of spammers and scammers?

The problem is this -- spammers have ways to disguise their IP addresses, they can change their IP addresses using rerouters, and some of them come from public IP addresses like schools or libraries or internet cafes, where blocking the IP address is not practical. YA does the best it can, under the cirstances. If a person is repeatedly suspended for violations, they seem to flag the IP and any new accounts that keep happening will be automatically closed within 24 hours. But that still gives these people time to annoy us for a while. Report, report, report is the only real answer.