It's been 20 years. Standards have changed. A Lot.
Each new companion is a custom model, a writer, new animations, and a voice actor at minimum. If each companion has their own companion quest, then it is designers, more writers, more animators and more actors, and much, much more time and money. We are just not in an era anymore where you can bang out generic companions in an after new with a junior staff writer and a portrait.
If Larian is going to stick to only five characters, then this is a pretty pathetic degree of variety. We have a chaotic evil rogue, a lawful evil gith, a cleric of an evil deity, a devil-dealing warlock, and a power-thirsty wizard. Not one classic hero (or even an interesting anti-hero...) in the bunch. I'd rather use hirelings than just about any of these assholes.
Please tell me we're getting hirelings.