It's simply more efficient to mandate three justifications. Think about it, if we only had one or two, we'd have to keep asking the same question over and over. But with three, we can just give up after the first one and say "oh, fine." Learn more about the Efficiency Justification
Redundancy is the new efficiency. The more words we use, the less words we have to use later. It's like the inverse of the old saying "less is more." In this case, more is more. Explore the Redundancy Justification
Because, let's face it, we've been doing this for years. And if it ain't broke, don't fix it. Or, in this case, do fix it, but only because we said so. Read more about the We Said So Justification