Your photos are not bad, however, they are not good either (for stock purposes) They are images and and having an image is better than not having an image at all. Something my photography instructor told me years ago.
Even photos that get accepted doesn't mean they will sell. I would highly recommend Tony Northrup's book Stunning Digital Photography, this book is a great help for beginners to advanced amateurs. There also some books to be found on Amazon really cheap that you can see what photographers are taking for stock which will help you develop your own style.
Don't give up, we all started somewhere and in no time you will see your acceptance rates move up and start seeing sales. Good Luck.