> US laid off employees also get 3-6 months of full pay and benefits.
Some employers may decide to give a few months of pay and benefits to laid off employees (although 6 months would be unusually large) but it is definitely not required and is not always done. Mass layoffs of 100+ people need to be announced 60 days ahead (but without naming who will be laid off) but there are no requirements for any kind of severance.
There's no legal requirement, but literally every company that is not bankrupt does it because otherwise they will face huge numbers of wrongful termination suits.