Perhaps Naruto has a big dream, like becoming Hokage. She might think that in a world where male leadership is more common, hiding her gender would increase her chances of being taken seriously. People might be more likely to believe in a male's ability to lead rather than a girl's, so she hides it to pursue her goal more effectively.
One possible reason could be that he is on a secret mission and doesn't want to be recognized. He might be infiltrating an enemy organization or spying on someone. Another reason could be that he has some new power or mark on his face that he wants to keep hidden until he fully understands or masters it.
He might want to protect himself. If others know how smart he is, he could become a target. Enemies might see him as a greater threat and go after him more aggressively.
Perhaps Naruto is waiting for the right moment to reveal his skills for maximum impact. He could be planning a big surprise for his enemies or wants to make a grand entrance at a crucial time. For example, in a major battle against a powerful foe, he could suddenly unleash all his hidden skills and turn the tide of the battle, which would be more effective than showing them off gradually.
Another possibility is that Naruto has a plan that requires him to keep his skills hidden from everyone, including Hinata, for a while. He could be waiting for the right moment to reveal them and use them to surprise and save the day, especially when it comes to protecting Hinata from a big threat that he anticipates.
Maybe she wants to avoid causing unnecessary worry among her friends and comrades. They are often involved in dangerous missions, and if they knew she was pregnant, they might get distracted. Naruto might think it's better to keep it a secret until she figures out how to handle the situation without disrupting their important work.
Maybe he wants to protect his loved ones. If his enemies know his true strength, they might target his friends and family to get to him. So, by hiding his skills, he can keep them out of harm's way while still being able to fight when necessary.
One possible reason could be fear of rejection. In the Naruto universe, he has so many expectations on him. If he reveals his true self which might be more vulnerable or different from the image people have of him, he could be shunned. For example, his experiences as a Jinchuriki made him an outcast initially, so he may be afraid to show more of his true self in case it causes more isolation.
Well, it could be that Sasuke has a personal goal that she believes is more achievable if she is perceived as a male. For example, she might want to rise to a high position in the ninja hierarchy, and historically, it has been more difficult for women to reach the top in that world. Also, she may be trying to fit in with a certain group or ideology that is more male - dominated. By hiding her being a girl, she can more easily blend in and pursue her dreams without the hindrance of gender - based discrimination.
Another possibility is that Naruto has his own plans and goals that he wants to achieve independently. His true power might be a key factor in these plans, and he doesn't want his parents' influence or interference. He wants to prove himself on his own terms, without relying on his family connection.
Another reason could be a personal journey of self - discovery. Naruto might feel that his identity as the hero of the village has become a burden or a limiting factor in his growth. Changing his identity could allow him to explore new aspects of himself, away from the expectations and responsibilities that come with being Naruto Uzumaki.