WHY ONLY 6X MAGNIFICATION?
The military have the money and the authority to order binoculars of any magnification they wish. They know (as does every binocular dealer and enthusiast) that the lower the power the easier it is to get good quality with a small binocular; the lower the power the brighter the image; the lower the power the wider the field of view. And the entire point of a binocular is to be able to see what is going on, there"s no point in having binoculars so strong that you can identify the rifle held by a soldier on a distant hill but not have the field of view to see his colleagues shooting at you.
This is why the standard strength for the infantry (and the smallest and easiest binocular to carry) is 6X. And the "powerful" binoculars used at sea (though these binoculars are always quite large) are 7X. They do have 10X, but a decent 10X (decent in optical quality) would be too large to hold and would be used mounted.
WHY EYEPIECE FOCUS?
Those who have become used to centre focus binoculars get to like them so much that they object to binoculars that are eyepiece focus. With centre focus you must turn the centre wheel to focus both eyes but have only one eye open (usually the left) then you must shut the left eye and focus the right eye by turning the eyepiece, then you turn the centre wheel again to focus both eyes together, first on something nearby then something far away, and if one eye is slightly out of focus you start again. Why people fall in love which such a complicated system I really don"t know, eyepiece focus is so much simpler.
With eyepiece focus you turn each eyepiece separately (focus the left eye, focus the right eye). All military binoculars use this system. The eyepieces on military binoculars will be marked clearly in dioptres (+ and - with zero in the middle for "normal"). You remember your dioptre number for each eyepiece then if you lend the binocular to someone and they focus it differently, you simply turn each eyepiece back to your setting when you get them back, no need to look through them, you now know that they will in focus for your eyes, so simple! And if you notice, over the months and years, that your dioptre setting is changing slightly, then you know it"s time to go and see your optician.
You may think that you have to focus binoculars continuously for near and far targets. Well, yes, you do with powerful binoculars, but with 6X the only time you will have to re-focus for distance is if you are looking at something very close. So if you are a keen bird watcher and you must be able to focus on a fast-moving bird as it lands a few meters away, then you may prefer centre focus.