Some of those folks are locked in golden handcuffs, some are expats on green cards, and some simply enjoy a less complex life of that comes with being a well-paid employee working for a well-known company.
Just to add more details on TNs if anyone read this, the visa is locked to the sponsoring company but it's possible to hold multiple TNs at the same time. Took me a while to figure that out. It can raise an eyebrow when crossing the border as it isn't regular to have more than one visa.
