I think for both it was more of a 50/50 call than it was definitive yes or no. Candelario had seen success, but also failure. He was only on the hook for one more season at most. Castro was still young and cheap, but had his issues.
And who knows, maybe they needed a fresh start elsewhere for themselves anyway. Maybe they don't see success if they stay in Detroit. But then that begs the question, what's going on in Detroit?