This is the barest of answers but you didn't get anything better, it's worth noting that many American military branches confer automatic pay grade advancements for eagle scouts. Additionally, until very recently many large American scouting functions (including the national jamboree, the largest American scouting function) were held on American military grounds.

More loosely, it seems that American scouting has a lot of the same stated ideals and interests as those that the US military looks to and even has some quasimilitaristic habits (like the treatment of colors). At least where I live right now, the highly militarized Northern Virginia/DC/Southern Maryland area of the US, scouts are often used as auxiliary workers for large functions like flag disposal and so have a lot of contact with military organizations early on.

Scouting also promotes leadership, venturing, etc that's highly looked for by recruiters. Since it's such a large organization its ubiquity shouldn't be that surprising.

I'm not sure how much of this has waned in the last ten years or so as the public image and internal image of scouting has seen so much scrutiny and change, though given the sub this is in I suppose that shouldn't matter that much anyway.