@Redknight-9, May i contribute with what i know?
From the looks of it, being Fleet Admiral is basically the next most dangerous job after being an Angel in this manhua universe. If they're not Angel, like how the other two fleet's admiral is an angel, they risk being assassinated either by corrupt subordinates, terrorist, aliens, or so on, or simply get caught in a crossfire like in this arc. This resulted in a situation where there are no more voluntary applicants for the position and all three fleets constantly in need for an admiral that is competent and capable, especially Beiyang, who's fleet admiral position is still empty at the start of this manhua (cuz the last admiral was assassinated by that Kangjin Planet's dictator).
When the MC accidentally applies for the position, it's safe to assume that both Beiyang's and 3-Legged Crow's higher-ups noticed his great resume as a renowned university graduate and his personal academic achievements which makes him a potentially very capable fleet admiral, hence why they both tries to recruit him as soon as possible. (Kunlun is probably too far from the MC at the moment to try to snatch him too)
And so in conclusion, the answer for why the fleets is treating the MC like a very rare and valuable asset is because he IS, in a sense, a very rare and valuable asset. He's like the only applicant of said dangerous position in a long time.