He made it political by granting him a hearing and considering the request at all. There was no requirement (or even precedent) for a governor to do so. The basis for his decision, as written in his five page statement, contained no information that was not available before the hearing or a matter of public record. In fact, if Arnold had done exactly ZERO in this hollywood-scripted-political-show, Tookie would have been executed, as scheduled.
We really don't know, do we? We can only guess at Arnold's motives. We have a difference of opinion.