Just had a thought. Based on this
Imagine if Nie Huaisang had been only a teensy tiny bit less careful. If Jin Guangyao had realized he was getting hunted, by who, and why. And realizing the trap had been laid so carefully and skillfully that there was no escape. That, in fact, Nie Mingjue was his only salvation. Imagine him diving deep and reckless and desperately into Wei Wuxian and Xue Yang's notes to find some way, any way, to bring Nie Mingjue back as a sentient fierce corpse.
That glimmer of hope despite all reason... After all, even if he were to succeed in putting Da-ge all back together again and with sentience like Wen Ning and Song Lan... Nie Mingjue was completely insane by the end thanks to the Songs of Turmoil and the qi deviation. Would FC!Nie Mingjue be sane? And even if he were, by some miracle of demonic cultivation... Why would he help Jin Guangyao? The man who murdered him slowly and then desecrated his corpse so he wouldn't be able to reincarnate? Why would Jin Guangyao believe that Nie Mingjue might spare his life, let alone save him from Nie Huaisang's vengeance?
Jin Guangyao is hanging all his desperation on the shredding hope that Nie Mingjue wouldn't want to see his brother cross the moral event horizon, and that Nie Huaisang wouldn't want his brother to look at him the same way he used to look at Jin Guangyao just before his death.