On the one hand I agree with you - when DM'ing I set DC's for Deception/Persuasion most of the time because it's easier than having a stat block for each random npc the players may want to interact with. Which is negated since you could have stats for everyone.
On the other hand, that may be too much randomness. Plus, unlike dnd, where every event happens once, I may be replaying the same moment in BG3 multiple times. So it would be weird for a low charisma character having an easier chance of deceiving than a high charisma character because the NPC rolled poorly.