Behind the bounty
Three bounties came back at the identical figure after Wano: Monkey D. Luffy, Trafalgar Law and Eustass Kid, 3 billion each. No source says why. The simplest reading is that the World Government declined to rank the three captains who had brought down two Emperors in a single night and issued them a flat rate: a number for the alliance, not for the men.
If so, the flat rate is unfair. Luffy put Kaido down himself, on the roof of Onigashima, after being reported dead twice in the same battle. But pricing that accurately would have meant explaining what happened in the final round — and there is little reason to think the Government wants that conversation in public.
The title attached to the bounty creates a second problem. An Emperor conventionally holds territory, maintains a hierarchy, and feeds thousands of men who take his orders. Luffy does have a fleet — 5,600 men declared themselves under his flag at Dressrosa — but he never asked for it, has never given an order to any of its seven captains, and rejects the idea of being their boss at all. He governs no island, collects nothing, and commands ten people and one ship. It's the first time the title has been awarded for capacity to cause damage rather than for a domain.
The same edition of the paper announced Buggy's promotion to the same rank, on a total misunderstanding. The two of them shared the front page: one had just beaten an Emperor, the other had accidentally recruited an army. The World Government priced them in the same issue, and that issue is a fair summary of the state of the world.
