>Wouldn't you just fire them for behavioral issue and poor job performance?
Employers use this excuse regardless of the actual reason though. Could be as simple as you took too many sick days or are up for more vacation days. It's a blanket for "we just don't think you fit in anymore." Mostly it gets them out of paying more towards their payroll taxes if they terminate you for cause rather than lay off. But they can't/won't deny you your UI, I think as a cop out in order to prevent you from suing for discrimination if applicable under any existing laws.