In this industry, when we get turned down, we don't always get a reason. Simply a “pass” or “no thanks” is often the only comment, and we're left to wonder why. Sometimes, if you're polite and ask in the right way, you can find out the thought process behind your rejection.
I recommend doing so whenever possible. It'll only make you better in the future. For now, though, I've compiled three common reasons you might not get signed.