For me, it wasn't an allure standpoint. The M16/AR-15 platform was one that I utilized with great effectiveness in the military, and the level of familiarity that comes from basically having lived with a rifle, even for the short amount of time that i did, meant that it was a primary and instinctive choice in a semi-automatic capacity.
Sure, DM's could enjoy the simplicity of a bolt gun, but even as I was leaving the military, they were being introduced to the AR-10 platform in .308, allowing for such an ease of transition that it was becoming a rare event to see a bolt gun in the hands of an operator, let alone a standard service member.
One more thing, in today's modern battlefields, an AR is the most appropriate tool a soldier can have. small, compact, lightweight and maneuverable, with a range of options and configurations, plus acceptance among the 5 branches of our Armed Forces, means that any AD personnel can put hands on a weapon and understand how to use it. We are not on the battlefields of 50 years ago.
(not trying to start anything, just offering a counterpoint to the above statement)