No citation was available at the time of posting, but presumably they were recognized for their proof of the Kadison-Singer Conjecture.
The George Polya Prize, established in 1969, is given every two years, alternately in two categories: (1) for a notable application of combinatorial theory; (2) for a notable contribution in another area of interest to George Polya such as approximation theory, complex analysis, number theory, orthogonal polynomials, probability theory, or mathematical discovery and learning.
The prize is broadly intended to recognize specific recent work. Prize committees may occasionally consider an award for cumulative work, but such awards should be rare.