That's strange. According to this report
https://sports.sina.com.cn/others/badmin/2021-04-27/doc-ikmxzfmk9260951.shtml:-
"男单资格赛共三轮,谌龙、石宇奇等直接进入决赛圈,而包括赵俊鹏、周泽奇、翁泓阳、任朋嶓等在内的选手参赛."
After three rounds of men's single qualification stage, Chen Long, Shi Yuqi advanced directly into the final rounds (main draw), including Zhao Junpeng, Zhou Zeqi, Weng Hongyang, Ren Pengbo and other players (translated).
Don't tell me Chen Long and the HK and Macau SAR players decided to skip the final rounds of the main tournament in September of the China National Games. For Chen Long's case, it may be that he's been chosen to skip and rest so that he is fresh for the Sudirman Cup also held in September; besides, he, now age 32, has already competed in several editions of the CNG previously, unlike the much younger 25-year-old Shi Yuqi who sort of can't afford to do so, not senior enough, therefore, not entitled to do so. Just my guess.
Also not forgetting Lu Guangzu, age 24, who is in the main draw of the CNG, so he's in the same situation as SYQ, which makes me think that he and SYQ as MS3 and MS2 respectively in the national team would be fielded in rotation during the Sudirman Cup, leaving Chen Long as MS1 to do duty most of the time. Again, that's just my thought.
As for the HKSAR and MacauSAR players (their absence or last-minute withdrawals), it's possible they might have chosen to give more priority to the Sudirman Cup than the CNG so as not to stretch themselves too thin.