Makes Playable factions less likely to join Confederations and Minor factions more likely to join Confederations.
Now compare this to Nestor("next" pic), This is also a trusted friend but it's Achilles(playable with unique units n stuff) and Agressive so he is far harder to confederate, later even his reluctance will be reduced a bit, but still he will stick with the player/against them for far longer than in vanilla.
I don't know about you, but Achilles used to be the most eager to confederate among the Danaans in my vanilla games. Probably because his holdings are the most exposed to super agressive trojans(I might look into that in a future mod).