They exist for the reason to liquidate them in case of national emergencies/severe economic crises. It's easier to liquidate these reserves when they are stored in trading hubs. That could be New York and London, or maybe even Shanghai, if China wasn't a systemic rival.
Storing all of them at "one's place" is a larger risk than splitting it up and storing them in several places, each with a different risk profile.
Does that happen often (gold sale)?
That exposes you to the risk of the country holding it. But for much of recent history, the US was seen as a lesser risk than a Russian invasion. Whether that is still the way the risks balance... I think we each may hold our own opinion on that.
Can't tell about the past where the risks of war with USSR were valid, but I think Russia invading Germany or Italy in the future is pure BS.
[Edit: First example I could find: https://www.newsweek.com/putin-ally-says-poland-next-ukraine...
I believe that Medvedev also said similar things, but I can't immediately find a link.]
Otherwise following the logic if Afd tells Merz not to jump from that bridge he should do the opposite.
Maybe there should be a real debate on that topic, or maybe Germany should even pursue such a repatriation of their gold reserves, but as a matter of fact there's no such debate or plan besides fringes parties, that's it.
This is as true in the middle east, europe, africa, south america or asia.