There are suggestions that part of the motivation was to reduce the power of the heavily unionized workers in Seattle and allow the company to transfer to a cheaper assembly plant in the south - just as car makers had done.
If you are only doing final assembly you can move the plant every 10years or so to get the best deal from local government. It's difficult to do that if you need an army of people with a lifetime of skills.
Boeing's goal, it seems, was to convert its storied aircraft factory near Seattle to a mere assembly plant, bolting together modules designed and produced elsewhere as though from kits.
of course it is still designed in Seattle, and many of those parts and outsource partners are still in the USA, only 30% is from abroad according to the article.
Contrast the positive adjective "storied," applied to the term "aircraft factory," against the negative adjective "mere," applied to the term "assembly plant." Reading only that sentence, it's quite clear which the author prefers.
a mere assembly plant, bolting together modules designed and produced elsewhere as though from kits