Keygens are a primary delivery vector for malware. Because keygens are unsigned, hackers can easily bind a malicious payload (like a Remote Access Trojan, or RAT) to the keygen executable.
ls ~/Library/LaunchAgents/ ls /Library/LaunchDaemons/ keygen in mac
You would be shocked at how many powerful, professional-grade apps are completely free and open source. Keygens are a primary delivery vector for malware