The House of Pharazonionath isn't losing Numenorean traits because they are Black Numenoreans, they are losing the Numenorean traits because the characters within the dynasty generally have pretty awful personality traits (from a LOTR perspective). The traits that degrade blood of Numenor traits are (in my experience) Sadistic, Lustful, Deceitful, and Callous, though there might be more.

Lore wise it's because as time goes by the blood of Numenor gets thinner as well as the fact that when the Numenoreans became less aligned with valinor and more with selfishness the gift of Numenor started to loose effect hence why the last kings of Numenor to die a natural death didn't actually live that long considering their ancestors and even Aragorn who lived thousands of years later

I do think, tbh, if you marry and breed with someone else who has the same Blood of Numenor trait, it shouldn't deplete as you're not co-mingling with others of lesser blood. But it's happening because of negative traits. Apparently, being an awful person makes it go down over time.

(Ngl, I use the console to fix that. They're not straight-up Numenorean as they're not from the island at this point, but they're still Pure. Especially if they're practicing intermarriage with family to preserve that.)

@GenuinelyEric
You're misinterpreting the entire poing of the uplifting of the Numenoreans, then. Their nobility is the entire reason that the Valar allow their uplifted bloodline to continue. That is why it seems especially strong in certain characters who just happen to be especially noble and and powerful of character (Isildur, Aragorn, Faramir, Prince Imrahil, Earnür)

They are no longer noble, hedonism, cannibalism, being an ♥♥♥♥♥♥♥♥ all decreases the chance of transferring Numo blood, the best you can hope for to reinforce back to pure numenorean blood through inter marriage outside the dynasty, but to get true numo either play Numenor sub mod is awesome, or make 2 custom characters merry them and then incest is wincst but also make sure you are just, brave, diligent, compassionate, avoid traits deceitful, sadistic, disloyal, witch is a huge no, cannibal? noooooooo! incest? nooooooooooo unless ... you modified your faith to divine marage, you better convert to ratious faith with avar pillar as well.

Originally posted by Space Wizard:

The House of Pharazonionath isn't losing Numenorean traits because they are Black Numenoreans, they are losing the Numenorean traits because the characters within the dynasty generally have pretty awful personality traits (from a LOTR perspective). The traits that degrade blood of Numenor traits are (in my experience) Sadistic, Lustful, Deceitful, and Callous, though there might be more.

It's right as you said.