Why would you give someone 6 months notice? What good is that for the employee? Especially if the severance is generous.
“Hey, we’re going to fire you in 6 months. Just a heads up.”
Nah. Give me the year of salary and send me home today. Better for the employee and for the company than pointlessly dragging it out. Again, this is assuming generous severance.
Job hunting takes time. Also, they won't be deported in 30 days, along with their families.
A "performance improvement plan" is almost always a 6-month/1 year warning that you're going to get fired/laid off.
It's common in some companies.