With regard to moving to Pullman, looking at it from a strictly practical perspective (not assuming any underlying motives), if he was set on doing a PhD, the process of finding a university accepting new PhD students into a program can be extremely difficult. It's not a case of simply applying and being accepted based on academic merits and an essay, as with a Bachelor's or Master's degree. To enter a PhD program, an applicant must first find a supervisor/advisor who has the capacity to take on a new PhD student and who is willing to work with the applicant over the course of their PhD. Some universities limit the number of PhD students a supervisor can have at one time (in my first job in academia I was limited to supervising four PhD students at a time, for example. Once one graduated, I could add a new one.) The applicant also needs to find a supervisor whose specific research interests/expertise closely match those of the applicant. This can get very granular and it's not a case of both parties simply being interested in criminology - the specific topic within the discipline and the research methods to be used, etc. are very important. Once the applicant finds a supervisor with the capacity and willingness to take them on as a student, they then apply for the PhD program and are usually admitted unless there are some glaring issues with their Bachelor's/Master's transcripts or test scores (not all programs require a test, but many will require something like the GRE or GMAT). On top of that, not all PhD positions are funded and getting a funded spot can be extremely competitive. Since BK was a Teaching Assistant, it seems he did have funding from the university for his tuition and a monthly assistantship stipend, so that could play a large role in deciding to go to WSU as well.
This is all to say that it's a difficult process finding a PhD advisor and program to begin with, let alone finding a school that offers you funding. Therefore, I assume having an available supervisor with the right area of research expertise + funding meant that WSU was probably one of his only choices. US News & World Report lists a total of only 42 university criminology programs in the US in its annual rankings, so there are not a lot of programs to choose from (and I'm not sure that all of those have PhD programs; some might only offer undergrad/master's degrees). To put that number into perspective, the same ranking site lists 493 universities with programs in business, so the number of criminology programs is very limited by comparison.
Disclaimer - I am a university professor who supervises PhD students and also completed a PhD 15 years ago, so I'm writing about this from my own personal experience with the hopes it provides some context into why BK might have chosen to go to WSU instead of staying in PA or in the East. I am not in the field of criminology, though. MOO