I get the sense that stronger alloys are more "brittle" and harder to do things like welding, as they'll crack instead of yielding from all the thermal stresses. This is probably the same sort of thing with laser melting and 3D printing: solidification under high thermal gradients. It seems this material is not only high-strength but also ductile enough to gracefully handle the thermal stresses.
It's more complex than that. A lot of the material properties depend on both the cooling and the tempering in aluminum alloys.
The phase diagrams for these types of alloys look wild (you often want to achieve
a certain material phase during cooling to "lock" in to get certain characteristics), and it can be difficult to ensure that the smaller metals participate during cooling. Also difficult to dissipate these slightly during tempering, typically to increase ductility.
This is probably why 3d printing hasn't been done in earnest, you can't design something within tight tolerances with unknown material properties.
3D printing of metals is being done in earnest, although the industry prefers the term Additive Manufacturing. Metal powder bed fusion is a stable, reliable process that is being successfully used commercially. It's generally confined to high-value applications that require extreme geometric complexity, but it can be invaluable in industries like aerospace, motorsport and medical. The range of viable materials is still somewhat limited, but covers a good range from titanium and aluminium alloys through to tool steels and heat-resistant super-alloys.
So you need to control the solidification process to plot a course through the phase diagram, spending the right amount of time in each region, and ending up in a good place. And this alloy has a phase diagram that is compatible with a method of 3d printing.
I think this is also why welding aluminum alloys was such a pain before the introduction of friction stir welding, which doesn't melt the metal. FSW was invented surprisingly late, in the 1990s.
