I think everyone has a dream guide, you just have to be willing and able to find them. Some people are very good lucid dreamers, but have no desire to find them, so they don't show themselves. And many want to find them, but aren't able to because they can't hold lucidity long enough.

There is no science behind it yet, so these are just my own beliefs. But I think DG's are the embodiment of your dream subconscious, which everyone has.