"But the US public saw this massive balloon and demanded it be shot down" You mean saw with their eyes or on the news? If it was with their eyes then it wouldn

"But the US public saw this massive balloon and demanded it be shot down" You mean saw with their eyes or on the news? If it was with their eyes then it wouldn't lead to public demand since as you say "weather balloons fly through our airspace all the time." and there's no way to attribute it to another country. If it's on the news then physical size is not relevant but detectability and newsworthiness are. People would have cared.