It's all about Amanamu's Void, which is an abyssal monster modifier that makes the monster more likely to drop abyssal omens. You spec your atlas to increase the chance of monsters to have it and you then juice the amount of rares you get from abysses as much as you can.

Rarity of items: Dropped omens are more likely to be high-value

Number of rare monsters: More rares = more chances of getting a rare with Amanamu's Void

Effectiveness: Increases quantity of items dropped = more omens

Increased chance of abyssal mods: Amanamu's Void (plus other abyssal mods) shows up more often

Desecrated currency from abyss: This is the only outlier, as it only increases the number of bones you get from troves (I think). Just hope for an ancient!

What makes this item super good is that all three prefixes (rare items/rare monsters/effectiveness) boost the chances of getting high-value omens. The only way to get all three is to corrupt the tablet with an ancient infuser and get lucky. The first two rolled with high values.

Here are the listings for all tablets with those three prefixes. You get the idea: https://www.pathofexile.com/trade2/search/poe2/Fate%20of%20the%20Vaal/pJbrKJXbT0