I don't automatically expect a particular prompt to be filled, but I do like responses on my prompts. I come here for the commentary and on-topic chatting and riffing about as much as I do the fanfic. If nobody responds to a prompt I'm proud of with so much as an "Ooh, interesting idea!" or a "LOL what would Leia think?" or some other comment to show that they've noted the prompt and liked the idea, I get a bit crestfallen and feel like I've thought up something not very good.

That's why I try to respond to prompts I like even if I'm not planning to fill them.