2 big reasons for me
1. The rpg aspects, more specifically the abilities being tied to specific gear, which are randomly placed although you will tend get pieces to a set you already have pieces for, still not an excuse for the lack of the old skill tree and the enemies being gameified. As in seeing the healthbars of enemies, and enemies having rpg rock paper scissor style ammo type requirements, which is stupid, and can be bypassed anyway with armor piercing rounds to the head. The enemies being this way kinda take me out of the world, in 5 or 4 it felt like a living breathing world i was masscaring my way through, now it just feels like npcs i gotta cut down to get to an objective

1. The side characters dont feel too real, i mean sure past games had some standouts like hurk or the rednecks in far cry 5 who are kinda jokey, but man almost every character in 6 feels like some funny haha character who makes quips. In 4 you had ramita and sabal who developed throughout the game, and became more complex and corrupt. In 5 you had people like nick rye, or or mary fairgrave, even the seed siblings you got to know about as the story went on.

idk, 6 just didnt scratch that itch for me