Because migration restrictions prohibit them from hiring those same low-wage workers domestically.

>And while you're at it, ask how companies justify that as a boon for the country they're moving to, then reconcile with the original statement.

Because those companies bring capital with them, increasing capital intensity in the destination country and thus increasing productivity and wealth.

Is it really migration restrictions?

Or is it arbitrage on minimum wage (which may not even exist somewhere else), environmental regulations, worker safety rules, etc.?

If developed western nations threw open their borders, they wouldn't simultaneously repeal all that stuff.