A brief explanation why…
Ranked as the 33rd largest supercomputer in the world at the time, the "Condor Cluster" was built by the US Air Force Research Laboratory using 1,760 Playstation 3s. Situated in Rome, New York, the system was constructed for radar enhancement, processing satellite imagery, and researching AI.
The console was chosen for its efficiency in handling high-resolution graphics as well as its its general affordability. While the PS3 was priced at around $400 at the time, it's reported that the AFRL was otherwise looking at an expense of $10,000 per unit for comparable technology built with conventional computer parts.
The PlayStation 3 was also ideal for its ability to run Linux, although this feature was removed in later revisions.
Prior to the AFRL's project, Gaurav Khanna at the University of Massachusetts Dartmouth physics department built a similar machine using almost 200 PlayStation 3s.