Thanks for this post! It’s an interesting perspective on some factors that might explain the coup. I’d just like to add a couple of things worth considering, based on what I know. I’m not very certain about how these factors interact with what you’ve written above.
(a) Personalities. A lot of the military’s decisions seem to stem from the personality and ambition of the top leader at the time. The military leader who initiated the shift to democratization in 2009/2010, Than Shwe, was sort of a wildcard and even military insiders were a little taken aback by his decision to democratize. Sanctions had something to do with it, but it’s far from clear that they were straightforwardly the impetus for the democratic transition. His successor of sorts, Thein Sein, proved to be much more moderate and reformist than almost anybody expected. The current military leader, Senior General Min Aung Hlaing, has not been shy about his ambitions to be President and has previously extended his reign on power past the mandatory retirement age to get the chance to be President of Myanmar. He was set to retire from the military after this last election and could have then been nominated by the military to be Aung San Suu Kyi’s vice president (there are two vice-presidents, one always nominated by the military). He’s reported to have hated the idea of working in a subordinate position to Aung San Suu Kyi. (b) Ongoing Civil Wars. While the country did democratize in 2010, many parts of the country have been undergoing civil wars of various types for several decades. The military is active and present throughout the country, controlling territory in part through official brigades, allied militias, and peace agreements with ethnic minority armed groups. I think the NLD’s power to frustrate military power and interests is limited and even after repeated electoral defeats, what probably would have been damaged is the military’s pride rather than its actual hold on power.
In any case, these are just some thoughts off the top of my head. Sadly, whatever’s happening in the country is a tragedy and will likely set back a decade or more of development efforts.
Source: a Myanmar politics class and my own Myanmar studies research work (sorry I don’t have any links on-hand)