I got 4 Lv. 100 Blue Dragons out of a single run two weeks ago.
You proably just have horrible luck with that stage.
The Red/Blue Manju stage did that to me on Nutaku, it took ~40 Runs to get the Flower gems from the 80 Stamina map.
The Yellow dragons balked me this week though. It took me six runs to get the two Lv. 100 I needed.