Sure there is: whatever reasons led them to build factories in the US in the first place.
And for, say, German automakers, they already have unionized workforces outside the US.
This whole narrative of "we cannot possibly try to improve anything for our people, because any time we do the wealthy overlords will move their business/money/etc overseas" is demonstrably bullshit, and always has been. It doesn't hold up for raising taxes on the wealthy, it doesn't hold up for unionization, and it won't hold up for whatever the next thing people like you try to use it to argue against will be.
And for, say, German automakers, they already have unionized workforces outside the US.
This whole narrative of "we cannot possibly try to improve anything for our people, because any time we do the wealthy overlords will move their business/money/etc overseas" is demonstrably bullshit, and always has been. It doesn't hold up for raising taxes on the wealthy, it doesn't hold up for unionization, and it won't hold up for whatever the next thing people like you try to use it to argue against will be.