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Because there’s nothing to be gained and everything to be lost from the US leaving NATO.
Yes, there are good reasons to develop an EU army with the same capabilities as the US but realistically speaking that’s decades away if we could start today but we’re not even discussing it seriously. In the meantime making any decision furthering the US from NATO gives no advantage to Europe.
It’s funny. You’re telling us that the technology was too complicated for some people to use, then you say we got to the point that it just works and you end with this being bad. Why do you think that?