What do you think they are after? Information gathering, and a diplomatic strategy where they pretend they are doing weather research, and see what others’ reactions are, and claim others are overreacting if they shoot them down, etc.
What kind of information are the Chinese looking for? I’m not cleared for that, so I won’t claim to know. Probably intercepting radio/cell communications. Maybe a contrasting viewpoint from what their spy satellites give. Possibly also actual weather research.
What gain are they getting? Again, that’s a strategic-level question, which I don’t think we have full enough info to answer. But overall, all major nations engage in intelligence gathering, and various sorts of diplomatic efforts. This is just one such program. It doesn’t really deserve the kind of political attention it’s been getting in the US, as seen in how it’s been going on for years with US intelligence services knowing about it, and not even bothering the US military with it.
Are they laughing at the US spending several million dollars to shoot down their inexpensive balloon?
– I don’t know if they’re laughing, but I don’t think it’s really cost the USAF anything. Those missiles have a nominal price under half a million dollars, but they don’t last forever, and the USAF test-fires them fairly routinely, so using a couple of them doesn’t really cost the USAF anything. It just gave them a more interesting target than they’d usually use in testing.