Because the crack needs to "patch" memory, it requires permission to inject code into running processes. This same permission allows malware authors to install a backdoor, turning your PC into a zombie used for DDoS attacks or spam distribution.
Ethical and legal considerations
Ironically, many "portable" cracks lie. They claim they don't touch the registry, but the Trikker loader frequently adds keys to HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Run to ensure a cryptominer starts every time you boot your PC. trikker torrent portable