Because Amercains bitch about "We can't build anything anymore" otherwise? Because a ready and well-practiced, upskilled workforce is important to a country, in everything to thr economy to wartime preparedness? Because Americans will continue to demand cars, and it seems pertinant to allow at least a path or two for a secure, national brand?
This is a tech forum. What happens when networking equipment only comes from other nations (that won't subsidise their industry either)? We end up having Huawei as the economic choice. A brand known for having deep ties to a political party that America is increasingly likely to enter at least a cold war with.
You're asking why supporting home-grown is bad like the last 4 decades of offshoring wasn't destroying what remains of middle Americans.