Cyber crime is a major source of income for these guys. It's not unlike having a bad password on your bank account. Also, malware is often configured by the op

Cyber crime is a major source of income for these guys. It's not unlike having a bad password on your bank account. Also, malware is often configured by the operator. If badguy1337 uses someone else's IRC bot code, they are likely to change the password themselves. Same for poison ivy, china chopper, and every other publicly available backdoor/shell.