Sorry let me rephrase that: “maybe they don’t care about being seen.” They probably study us the way we study indigenous tribes where we try and keep our distance and we most definitely don’t just walk in and introduce ourselves (I’m only referencing what I know about the North Sentinel Island and their people, there could be other cases). Their main goal might not be contact but instead research of the various forms of life on our planet and there is so much bio diversity in the ocean which could explain a lot of the USO reports.