Refining capacity near Entebbe, combined with direct air links to Gulf trading centres and a permissive early licensing environment, pulled regional gold toward Uganda over the past decade. Geography did the rest: several producing neighbours have weaker export infrastructure.
Hub formation of this kind is generally sticky once established. Traders, freight forwarders and correspondent banking relationships build around a route because the route works, and switching an entire regional flow to a different jurisdiction requires more than a marginal cost advantage elsewhere; it requires the alternative route to be reliably cheaper and less risky for long enough to justify rebuilding relationships from scratch.