There's more that can be said here about the designs of NATO specifically, but in the meantime here's an answer I wrote last year on why the US pursued bilateral alliances with Japan and South Korea rather than a multilateral grouping.

https://www.reddit.com/r/AskHistorians/comments/njdkwi/why_did_the_us_favour_a_multilateral_defense/gz8r5gp?utm_medium=android_app&utm_source=share&context=3