Hey maybe, just maybe one I can answer. I've never had a whole lot of success posting on this sub, which makes me love it even more.

Okay, so I guess I need to explain how I know about this... My dad was an infantry officer in the US Army between 1974 and 2006. He enlisted, hit sergeant, went to college, became and officer and retired as a Major. This obviously led me to at least a passing interest in military history and I took courses throughout college. I have "some" government experience that involves warfare but I have never personally served in the military, i.e. I've never had a rank. Swore an oath though.

So to answer the question...

The answer is that it's not really considered a practical text on military leadership and strategy. The book was written in 500 BC so it's not necessarily as practical. Is the book on the recommended reading list for West Point? Yes it is. https://blog.refactortactical.com/blog/west-points-recommended-reading-list/ But it is more considered a part of the history of warfare rather than a guide to how to execute modern warfare.

I mention the present to show how the book was received in the first Western-language version, which was in French, I want to say in the late 1770s. So, guns were already a thing in combat. The first English translations didn't hit until the 20th century.

To see what I mean about the practicality of Sun Tzu's advice, much of which is pretty standard for officer training, just look to the "9 Terrains" chapter. It's interesting but limited to a man who had only seen Asia, as vast and diverse as that terrain is, at a specific time. By the time English translations were becoming available, a new generation of officers was wondering how airplanes would affect combat. Sun Tzu never thought of that.

Maybe this is a little too far down but the introduction to the history behind "The Art of War" written by Victor Mair (had to delete a link here, I didn't realize that apparently it was a pirated version, my apologies) notes that information spread at the time meant that Sun Tzu was not widely known among Western audiences until much, much later than we realize. For example, the Japanese translation wasn't done until 1750!

Mair also notes that it was a Jesuit priest that published the first French version in 1772. He goes on to further note that the modern popularity of Sun Tzu seems to be linked to a rumor in the 20th century that Napoleon had read the French translation and used it to help conquer Europe. No evidence Napoleon read the Art of War has ever been presented as far as I know and Mair straight up debunks this while probably giving the most direct answer to the original question:

"...although there was some notice of Amiot's translation in French literary journals when it was first published in 1772, the book soon dropped out of sigh so far as the general public was concerned..."

Basically, the only people that cared at the time were people already interested in China.

Did I do it right? If I need to edit or add some more links, let me know. I'd love to actually answer a question on this sub!

EDIT: I did have to make some changes to abide by community guidelines but nothing too bad other than a faux pau. Thanks so much to the kind stranger that gave me gold and I'm really happy I finally got to contribute to a sub I've been lurking in for so long. I've had a rough couple of weeks so this stupid little post that I almost didn't reply to because I was so tired from work, makes me really happy.

All the best,

Andrew