The game theory of the balloons
One possibility is that the Chinese simply have been making a stupid mistake with these balloons (it is circulating on Twitter that this is not the first time they sent us a surveillance balloon — probably true).
A second possibility is that a faction internal to China wants to sabotage better relations between the U.S. and China.
A third possibility — most likely in my eyes — is that we do something comparable to them, which may or may not be exactly equivalent to a balloon. Nonetheless there is a tit-for-tat surveillance game going on, in which the two sides match each others moves, and have done so for years. The game evolves slowly, and occasionally all at once. The Chinese have been playing by the rules of the game, and the U.S. has decided to change the rules of the game. We may wish to send them a stern signal, we may wish to change broader China policy, we may think their balloons are too big and detectable for this to continue, USG might fear an internal leak, generating citizen opposition to balloon tolerance, or perhaps there simply has been a shift of factional powers within USG. Maybe some combination of those and other factors. So then USG “calls” China on the balloon, cashes in on the PR event, and simultaneously de facto announces that the old parameters of the former game are over. After all, in what is more or less a zero-sum game, why should any manifestation of said game be stable for very long? It isn’t, and it wasn’t. Now we will create a new game. A very small change in the parameters can lead to that result, and in that sense the cause of the new balloon equilibrium may not appear so significant on its own.
It was also a conscious decision when and where to shoot down the balloon.
Here is some NYT commentary, better than most pieces though it neglects our surveillance of them.