I think it's just because most people haven't heard of it. Telling someone (like a friend) about it can get mixed results- I've had people basically tell me I'm crazy or think I'm really weird. Now, when I want to tell a friend about it, I describe it as if I don't know it's an actual thing that people practice. I'll bring it up like, "What if this was a dream?" Or "What if you were dreaming and you knew you were dreaming- you could do anything, wouldn't that be weird?" People tend to "accept" it more as just a concept. One friend that I told about LDing this way has actually had several lucid dreams since then, and always tells me about them! So I guess it has a lot to do with how people tend to be wary of new things or ideas that aren't really accepted as common (yet.)