This is all rather besides the point because EU4 is a game about roleplaying as a state in the early modern period, and pre-state societies really have no business being playable on the same terms as the rest of the game
EU4 is about more than that. That's one of its stated goals. Another of its stated goals is to be a fun and challenging strategy game.
There are players who are interested in a compromise between both of these factors, and there are players who are mostly, or exclusively interested in only one or other. I assume you're primarily interested in the historical aspects. I am one of the players who is exclusively interested in it as a game. I couldn't care less if a feature is historical or not, so long as it adds to the strategy, challenge, and fun.
Unfortunately the needs of the two groups are very often at direct odds with each other. Paradox seek to find a compromise, and are sometimes successful, sometimes not. It's therefore as well that whatever camp we personally fall into, we remember that the other camp exists and that therefore some things will not always be modelled in the perfect way for our preference.
This is one example. It may well be totally unrealistic for pre-state societies to have inflation, and no doubt a number of other concepts. But removing them in the interests of historical plausibility may very well negatively impact the game-playing aspects.
I believe that any argument made against the game that starts out "This is totally unrealistic" then needs to go on and ask "..but does it improve the strategy/gameplay/fun." Because if the answer is yes, then that's likely the reason it's there, rather than Paradox just not caring if things are historical or not.
I make these points somewhat generally, in response to your implication that the game is
just about roleplaying a state.
But in this specific case, with inflation being a rather minor, even insignificant part of the game, it's quite likely that the arguments are neither historic nor about gameplay.
I expect they simply don't want to spend further development time making exclusions and special cases for a mechanic that doesn't much influence the game anyway. No doubt they feel that the new tribal mechanics, including many tribal-only features, are enough to distinguish the tribes both from a historical and gameplay perspective.
As a strategy game player, not a "state roleplayer", I fully concur with that: I want them to spend time on bigger features, not removing inflation from pre-state societies.
You might be able to mod it out, if you continue to feel strongly about it.