@FluttershyLabeouf: It's difficult, but I think it's important in solving a reoccurring issue like this. There has to be something that prevents you from completing your stories, even if you don't know what it is yet. If it helps any, my issue was, and still is, the lack of a "good" plot. I believe I must have a solid story before I can write it, yet I'm not creative enough to make one up.
Have you tried just writing out the "fun" parts and filling in the spaces later? Or writing backwards (starting from the ending instead of the beginning)? Some people find it easier to work non-linearly, like myself. The very few stories (that are all less than 10k words) I've completed were done using the "skipping around" method, in fact.
What about limiting yourself to a single, larger project, instead of trying to make every idea into a new one? Challenge yourself to work interesting ideas into an established plot, this could help you focus, instead of splitting your attention.
You could also try world building if you can spare the time. It's a time consuming process, but exercises your commitment and creativity while also providing you with a framework that you can put your stories in.
