It could be to gradually increase reaction expectations so it would not be surprising if China shot down one of the USA's drones. Or perhaps escalate by using their previously demonstrated ability to blow up satellites. The balloon was a very public microaggression that forced the USA to respond in a very public way. China tried the public "oops it was a weather balloon" to give the USA a chance to back off the public response (but know that China was still provoking them). But it was too brazen to accept.

The USA is already on their doorsteps by having bases in almost all the neighboring countries, and conducting operational freedom exercises by flying and sailing through disputed areas.