Backstory: A story that tells what leads up to the main story or plot.
I have heard other others, agents and editors say that your backstory should be given in small increments throughout the story. It is strongest in dialogue.
The backstory is mainly for the writer so that he/she knows where the characters have been and what has brought them to this point. Yes, the readers may want to know this, too, but they want to get immediately into the action.
And agents and editors will rarely pick up a manuscript that has an introduction.
Remember you want to make an editor/agent and reader care about your main character right away. You want to grab their attention with your first sentence.
Yes, you see these problems in many stories that are being printed today and over the years. As with everything follow your instincts.