I can't speak to why it's a seemingly popular subject, but how much have you read in the field, exactly? Firstly, the classic "where are your troops and may I count them" question you posed can be answered in a few minutes with Google. The number of airplanes/tanks/ships we have and specific characteristics about them isn't some state secret, and the government puts out plenty of its own academic research (via war colleges, officials working in and out of think tanks, etc) to provide this information to academia. So to answer your question, such data is readily available to those who seek it.
Even so, you're only describing a small part of the field. It's not like security scholars sit around a table "Dr. Strangelove"-style and fantasize about how to start another war; in fact, there's a lot of dry theory involved in how states act within the international system to meet their own national interests, or even a lot of crossover with how economics, cultural aspects, etc affect the security realm. Much like other fields of IR, you can really fit security into almost anything.