What is with the silly and annoying AIs

Such as Roland’s obnoxious costume or Isabel’s eccentric personality, or Halo 4’s overly emotional/Halo 5 arbitrary evil Cortana.

Compare that to old Cortana who is rather normal and relatable, or HW Serina who was sarcastic or Reach’s Dot which is a typical AI.

Why do they have make AIs so generic and absurd.

The AI were always eccentric. Maybe you’ve forgotten, but Cortana was always a highly sarcastic naked blue woman. and her development through the story does have lore explanations covering her transition from Halo CE through her demise in Halo Infinite. I don’t think your assessment reflects the reality of the AI in Halo lore.