They've been doing it for a few years. The US did it in the 50's. The reason we're talking about them is two fold: 1) the "first" one had such a massive payload that people could see the object from the ground. People were posting a bunch online even before the media picked it up. 2) It became a political issue about the US's strength in response to China. That amplifies the former to be a larger and broader discussion(s).
This could also indicate China's surveillance capabilities. Need to use balloons to get high resolution rather than relying on satellite imagery (kinda why we don't really use U2s anymore and why that Trump tweet was seen as a big deal). It could also be trolling. It could also be testing (including of cameras that would be put on satellites). It is hard to say anything with certainty tbh. Militaries work in secrecy and that's why information is so valuable (despite what many think). But the objects will be recovered and you'd be surprised what can be reverse engineered from an exploded pile of scrap.
This could also indicate China's surveillance capabilities. Need to use balloons to get high resolution rather than relying on satellite imagery (kinda why we don't really use U2s anymore and why that Trump tweet was seen as a big deal). It could also be trolling. It could also be testing (including of cameras that would be put on satellites). It is hard to say anything with certainty tbh. Militaries work in secrecy and that's why information is so valuable (despite what many think). But the objects will be recovered and you'd be surprised what can be reverse engineered from an exploded pile of scrap.