Four generations of Huo Ying didn't teach Kakashi to drive Raytheon, because Kakashi could use Shenwei in Kishimoto's setting.
Kakashi and Feng Shui Men are both supporting roles in Huo Ying's plot, and their collocation ability is naturally limited. Watergate doesn't have many ninja attack skills in the plot, so Kishimoto Watergate is designed to master Raytheon. Otherwise, the skill configuration of the four generations of Huo Ying will be too simple. Kakashi's failure to learn to fly Raytheon is not a problem of lack of talent, because Kakashi's talent is not good enough to figure out how to use Shenwei as a space skill, but a requirement of skill design balance, because Kishimoto can already foresee the future use of Shenwei after bringing sharingan to Kakashi.
In Huo Ying, no character can master two spatial transfer skills at the same time, except the big barrel wood (the big barrel wood can use Tiangong and Huangquan), so if Kakashi masters two spatial skills, his personal strength is too strong, and he is suspected of usurping the master role.
Flying Raytheon consumes chakra very much and is not suitable for Kakashi's study, because sharingan consumes too much for Kakashi's chakra.
Many people say that four generations didn't teach Kakashi Raytheon, mainly because Kakashi chakra was not enough. Personally, I think this statement has some truth. Kakashi can't control the opening and closing of sharingan freely after transplanting sharingan with pictures, so the sharingan of Kakashi has been in an open state.
Kakashi doesn't have the special physique of Neiguang team, so he naturally consumes chakra much faster than ordinary characters. Flying Raytheon is a skill that requires users to have a large amount of chakra reserves to use. Therefore, after Kakashi got sharingan with a picture, Watergate thought that learning Raytheon would not increase Kakashi's comprehensive combat effectiveness, and might even drag Kakashi down, because if chakra was insufficient, forcibly using Raytheon might kill users.
After Kakashi got sharingan, chakra consumed much faster than ordinary characters. Therefore, in order to protect Kakashi, Watergate didn't teach Kakashi the endurance skill that requires huge chakra.
Finally, to sum up, I personally think that the reason why Namikaze Minato didn't teach Flying Raytheon to Kakashi is the need of the plot, and Kakashi's supporting role should not be too strong. The second is to protect Kakashi, because Kakashi has the chakra in sharingan that can't stand the consumption of Raytheon. Please forgive me if the analysis is not in place. If you have other ideas, please leave a message to discuss.