Because it's cheap, not because the US or Europe don't know how to manufacture ASIC.
So they are going to somehow set up a "major manufacturing plant" to create ASIC that *no-one knows about* in order to attack Bitcoin?
Seems a little far-fetched to me (western governments are not so good at hiding stuff like eastern ones are).
It's no more far-fetched than they spending astronomical amount of money to attack a PoS system (and without guaranteed success, like attacking a PoW).