The most frustrating thing for me is that they don't tell me why they rejected my writing. Is it bad? Is it off topic? Is it simple-minded? Is it too complicated? Is it... I don't know... whatever?

I know editors don't always have a lot of time, but anybodies writing would improve with a little feedback. I, too, have little time, and need to make what time I do have meaningful and, hopefully, remunerative. I'm perfectly willing to give an editor exactly and precisely what they want... and believe I'm quite capable of doing so... I just have no idea what it is they want.