I don’t know why these people are coming up with these strange, otherworldly theories. The simplest explanation is also the most likely one. The free world is fairly open about civilian airspace usage. Nobody watches civilian-looking craft wafting through their airspace. Chinese spooks saw an opening and drove a semi through it. Hacking, balloons, tourists, students, academics, businessmen - they throw stuff at the wall, and some of it sticks.
Some time back, I read that over 90% of Chinese airspace was reserved for military use. If Wikipedia is to be believed, that number is now 70%.
https://en.wikipedia.org/wiki/Civil_aviation_in_China#Air_traffic_control
When I set foot in China for the first time ever decades ago, I assembled a tripod to get a shot of a scenic riverfront view. Some random passer-by started hassling me, like I was a spy lining some installation up for an artillery fire mission. (Was he a plainclothes security guy? If so, he was a really convincing civilian, dressed like a day laborer). I hastily folded it up and walked away, lest he sic the local gendarmes on me.
I wouldn’t doubt that the PLAAF is similarly angsty about any civilian intrusions into airspace they view as theirs by right. This sentiment is entirely missing in the free world. That’s why the Chinese balloons slithered their way in. Because outside of China, no one monitors civilian craft away from airline flight routes, let alone shoots them down. It would not surprise me if the balloons had been doing their thing in US airspace for many years prior to the recent discovery and shootdown.
“It would not surprise me if the balloons had been doing their thing in US airspace for many years prior to the recent discovery and shootdown.”
I think the Pentagon or NORAD has already admitted that.