Did you ever see those old writing contest threads where the whole thing fell apart because the prompt was too loose? I remember one from a few years back, the prompt was just "write about loss" and almost nobody entered, but the next month it was "a suitcase left on a train platform" and the thread blew up with like sixty replies. There is something about a concrete thing that gives your brain a hook to hang the story on, and without it you just sit there staring at the blank page. The 47 word stat makes sense to me because once you go past a certain point, you are basically writing the story in the prompt itself and there is nothing left to figure out. I keep a little note on my phone of single images I come across, a cracked windshield, a dog waiting outside a store, and every time I use one of those I get way more done than when I start with some big idea. It is funny how the smaller the prompt gets, the bigger the story becomes.