Ty TJ. No reason other than "they" say so, so that makes sense.
While in the Army, I had to do the Expert Infantry Badge a few times. We had to carry 35 lb rucks (packing list enforced and weight checked prior and post march), helmet, weapon, web gear and had 3 hrs to complete 12 miles. And for some reason, they always held it in spring/summer, so you got the full benefit of the lovely NC weather.
Something you may not know, knee high women's stockings work really well under socks to prevent blisters.
Yeah, in the Navy we did a lot of stuff "just because". Including the ever-popular "Hurry up and wait".
We didn't really do any rucking anywhere, but we did run endless miles around a giant paved area we called the "Grinder" and do countless pushups, situps and jumping jacks.
I mentioned the stockings thing to my wife and she grinned and said "Really?".