Why were they chosen? I'm not saying you have to like them. It is very subjective for us all, writers and judges alike. That is clear from the fact that you can have a story rejected by several publications/competitions, but snapped up by the next one you try. What one person loves, another might loathe.
But, like them or not, you have to accept that the winning stories must be very publishable. They have been chosen. They are outstanding. They are better than everyone else's entries, including yours. Another judge on another occasion might have included yours, but this time you didn't score as high as the selected few who were placed. So it is vital that you study their work and find out why.
Look at the opening, the portrayal of the main characters, the way the plot has been woven, the use of language, the dialogue, the 'show don't tell' factor, the ending. What was the theme? Can it be summarised in a few words? That is often the key to a good story. If you have to wonder what it was all about, then it doesn't work as well.
Now look at the story you entered. How does it measure up? Then work on any improvements. Some will be immediately apparent. Do your rewrite. Then send it off somewhere else as soon as you can.