Master Keys haven't shot up in price like they have in the past. Unfortunate for me - I spent all my EC on my main to get keys early to sell at a gain
I guess between the low dil:zen price and the key sale, people aren't wholly depending on the Exchange for keys.
Also, it seems the boxes drop less. Probably not true, but maybe. I did two combat missions and a couple STF's, and only got one box. Heck, I've only gotten 20-30 boxes total in the last month, when I used to be able to do that in less than a week.