Interesting, as I do just the opposite. Given a choice, I go long cage, as it gives me flexibility in the future if I start changing gearing. Now some of my RDs are short cage, they tend to be vintage parts that I wanted to use, so I accept the limitations.

+1 To below, I am less locked in my gearing, so I tend to change things up. If I was locked in, might as well get the shortest cage that does the job.