Board Thread:Naruto Discussions/@comment-33485854-20180923223009/@comment-25607614-20180924204225

It's important to take in to account that Kakashi becomes the Hokage directly following a war in which the greatest shinobi in history were returned from the dead and brought to bear against the living ninja of every village.

We didn't see everything that happened, but we know Shikamaru and Ino's dads got chunked pretty hard. We also saw what just Madara did to an entire army of shinobi. If we infer from those scenes that there was a fair degree of casualty, then Konoha, and all of the villages would have been hurting for man-power and making swift promotions to fill the gaps left by the dead ninja.

You see it a lot in real-world wars. Low-ranking soldiers getting promoted just to fill gaps. Konoha would probably actually really need it, since they had that attack by Orochimaru. Then Pain. Then this war, all in fairly rapid succession.