Well, yes, but you can figure those things out if you give a mere 10 minutes of thought to them. And if you're a military commander in charge of peoples' lives, you would be an idiot not to spend that requisite time doing so.
And yet it's amazing just how many and how often people disregard any and all of it, to their detriment. Beyond that, some times you don't
have ten minutes to make a decision. Having internalized a set of maxims (be it from the Art of War or otherwise) that will more likely than not at least lead to a less disastrous outcome... it can help.
Beyond
that, we
still live in an age when "Where abstract thought doesn't exist, and learning is done by experience." is a truism for a great many people, including those in power. Many -- most, most likely -- people are never
taught particularly involved degrees of abstract thought, and never stumble upon it naturally or only do so (much) later in life. For them, a "Don't be an idiot"
guide is... pretty damn useful, and for many more people it's useful before they actually know enough to
stop being an idiot (I.e. young and stupid). I've met quite a solid handful of folks that have been forced to read Tzu's work in depth and came out better people, by their own admission. Because, y'know. Lotta' people tend not to think until prodded, but once prod, cannot be unprod.
Point being the Art of War, along with a number of other military guides of such nature, should honestly probably be required reading in, say... middle school, maybe late elementary? And then again in mid-late high school, and likely
again in early college. Especially if used in contrast or support of more peace-related texts, probably part of a general critical thought regimen. I've... met more than a few folks it probably would have helped. Likely would have been a bit better off m'self if I'd been in something like that when I was younger.
Plus, damn. Who
wouldn't want a week dedicated to what the proper point to set things on fire is? S'shit like that that's how you catch the attention of youngin's