You can't send a balloon with any degree of accuracy, hence why the spy claims are ridiculous. However, you can send it in the air streams that have predictable patterns due to Earth rotating. So you can put a balloon up in the upper atmosphere and have it drift around the world with high likelihood of eventually making it over some part of US. Incidentally, US did this themselves to China back in the 50s https://theintercept.com/2023/02/07/china-balloon-soviet-union/

Another reason China wouldn't send a spy balloon is that US obviously has the capability to shoot the balloon down and would almost certainly do so. China wouldn't want to give US access to any actual spy tech and learn their capabilities.