Imagine you have just built a house and every day someone knocks on the door to suggest a color of paint or some sort of furnishing. One day it's pink and you look around—bathroom, bedrooms, closet—and think, No, pink just isn't right for me, it doesn't fit with the house. It doesn't match how I want the house to look and feel. Someone brings cream, which is fine but not exciting. Another brings purple, which is much too much. So it goes.
I'm heading toward the beginning of my fourth year of editing/producing *82 Review and my millionth year of sending out stories and poems (I swear it's true). So I'm on both sides of the submission rejection/acceptance fence. The rejection phrase, "not a fit for our magazine" annoyed me until I came up with the above metaphor of house and paint. Although I don't use those words when I decline a piece, I now do understand it.
Each editor has a vision, a house, that s/he is furnishing. Sometimes that poemtable is nice, sometimes even extraordinary, but it's not the right style for the issuehouse. Each submitter also has a vision and style. Sometimes the subject or form matches the editor's vision and style, more often, it does not. Think about your friends, how you met them, the people you met and liked but somehow the friendship didn't gel or you didn't keep in touch. Your piece and the editor need to have the right chemistry and intention for a longterm match.
Maybe you've heard that it's all subjective. It is. It really is. Keep writing. Keep sending. Try different places. Eventually, you'll knock on the door that opens to you. And your piece will finally fit.