Earlier quoted context omitted.
I find this question distasteful, since it's asked with nothing more than a vague insinuation of Viazovska potentially not being "that good" as motivation. Here's the long citation: "A very long-standing problem in mathematics is to find the densest way to pack identical spheres in a given dimension. It has been known for some time that the hexagonal packing of circles is the densest packing in 2 dimensions, while in…
So what's so special about 8 and 24 dimensional space?
What we know is that these dimensions support lattice structures with exceptional symmetries. The intricate geometry of these symmetries interacts with number theory to provide spectral data (automorphic forms) that have very rare properties; this is the starting point for Maryna's investigations.
Okounkov's popular scientific exposition "The magic of 8 and 24", linked in the article, goes into considerable detail on the constructions.