This article from National Interest.Com, discusses how ATAK is different than most DoD programs, and some of the reasons for its success. From the article:

ATAK also provides a fairly wide variety of map tools, driven by the feedback of its users. These include the ability to see elevation along a planned route, the ability to measure distances to locations on the map and the ability to overlay graphics over the map as layers. All of these are fairly advanced features, which while common in the civilian world were something military navigational devices often lacked. ATAK also includes targeting and runway survey features in its military version, which allows for observers and reconnaissance troops to work more efficiently.

While ATAK is compatible with a wide range of devices, the small form factor of a modern smartphone running Android is probably another reason for ATAK’s popularity. Special operations troops are often spotted with a rectangular mount on their body armor above their magazines. This is a fold-down mount for an Android phone running ATAK, which is often all that is needed to operate effectively with it. This stands in contrast to the bulky, wired up wearable computers that were in earlier future soldier programs.

ATAK has even seen use in civil and law enforcement applications, under the less aggressive name “Android Team Awareness Kit.” The same team communications, navigation and mapping capabilities are useful in many outdoor jobs, including wildlife surveys, forestry and geology. ATAK’s ease of use is a large factor in its widespread adoption, tactical units in the Department of Homeland Security were able to get most troopers trained on basic functionality within five minutes.