I think there are three reasons for this: firstly, people who know the inside story won't tell it, secondly, people who don't know it really don't know it, and thirdly, Hua Mulan disguised herself very well. So no one could recognize that Hua Mulan was a daughter, and people didn't expect General Hua to be a woman. Hua Mulan was born during the Northern Wei Dynasty, Xianbei people, at that time, Liu Song in the Southern Dynasty and Zoran in the northern grassland were the main enemies of Northern Wei, but the biggest threat to Northern Wei was Zoran. Northern Wei period, the implementation of the Hu-Han partition system, from the army to participate in the war is the Xianbei people, cultivating land grain is Han people, Hua Mulan family is a military family, ancient times, the war conscription are recruited from all over the country, the same local people into a battalion, more than one battalion into an army, so Hua Mulan into the battalion of the people are all her fellow townspeople, her townspeople, although they know that Hua Mulan is a woman, due to the fact that, from early childhood onwards, Hua Mulan love to Since Hua Mulan had loved to dance with swords and clubs since her childhood, she was very good at martial arts, so no one said anything about it. A battalion of her countrymen would follow Hua Mulan into battle, so that they would have a better chance of surviving on the battlefield.
On the battlefield, Hua Mulan's achievements were remarkable, with twelve military honors***, and Hua Mulan's name was written on the military honors booklet, so Hua Mulan was promoted from a soldier to a general. After Hua Mulan became a general, she had her own separate tent, and her fellow countrymen were her personal guards, so no one mentioned the fact that she was a daughter anymore. When Hua Mulan fought with the other Wei troops, she only met them in the army, and usually they fought alone, so no one would think that General Hua, who was so successful in battle, was a woman. Hua Mulan herself had a separate tent, which could solve her personal problems well, she did her daily washing and laundry herself, and when someone came in, her own soldiers would inform them in advance, so no one else thought to think that General Hua was a woman.
Zoran was a nomadic people, and they rarely assembled an army to meet Northern Wei head-on in battle, sending small detachments to pillage Northern Wei border cities. So Hua Mulan led her troops to start a guerrilla war with the Zorans at the border, you sneak attack me, I am going to attack you; you retreat, I chase you for a while; you come to attack me, I will hold on to my camp and not come out. Wars and attacks on the fortresses of the enemy and our armies took place almost every day, and though they were all on a small scale, they occurred frequently. Soldiers hear the horn to meet the enemy to go to war, when there is no war, they rest, who has time to think about the identity of General Hua Mulan, naturally no one suspected Hua Mulan gender issues.