Pure metals are soft, because all their atoms have the same size, so the atom layers can slide over the others.
Mixing metals with different sizes increases the strength, because now the atom layers are no longer smooth, but they have bumps, which prevent sliding.
It can be shown that mixing many different kinds of atoms, taking from each about the same quantity, can provide very good mechanical properties, because the bumps in the atom layer will be frequent and they will have varied sizes and a random distribution, which will prevent any alignment between bumps, which could facilitate the sliding of the layers. Think about how to design an anti-sliding shoe sole. Random bumps of random size would give the best result.
The so-called "high entropy" alloys contain at least 5 different metals, with about the same quantity from each.
However the alloys that contain almost equal quantities of each component are very expensive. In order to make a cheap alloy, one must have one or at most two components in a much larger quantity than the others, so that the abundant components can be chosen from the few cheap metals, e.g. iron, manganese or aluminum, while the other components, which are added in small quantities, can be chosen from expensive metals, like nickel and cobalt.
For this reason, the better "high-entropy" alloys are normally replaced by the cheaper "medium-entropy" alloys, which use 5 metals, like the "high-entropy", but which are used in quite different quantities, with larger quantities from the cheaper metals, if possible.
The use of "high-entropy" alloys and "medium-entropy" alloys has begun only relatively recently. They are used to replace the cheaper classic alloys only when they offer a decisive advantage that can justify their higher cost.
This case is one such example. From the classic aluminum alloys, some of the weaker alloys, like AlSi or AlMgSi can be easily 3D printed, but they have low strength. The classic high-strength aluminum alloys cannot be 3D printed. Therefore this was a clear case when a newer kind of alloy must be tried, if high strength is desired. They have experimented with certain kinds of medium-entropy aluminum alloys, to keep the cost acceptable (and also in this case the high content of aluminum keeps the density low and the conductivity high, which are frequently the reasons for choosing an aluminum alloy), and the results were good.
Nevertheless, this alloy is likely to be several times more expensive than AlSi or AlMgSi, so it will be used only when its high strength is necessary.