Because most of the benefits are not immediate and are public, rather than private in nature.

Most people don't really care about, or even think much of, how their choice of money affects the public sphere--they're just interested in getting through life, and Bitcoin just doesn't really help with that right now. Unless you count the potential for "number go up", but we know that's not reliable on any predictable timescale.

Combine that with how most people are quite allergic to technical jargon... and there isn't yet a user-friendly app that lets you start earning and spending bitcoin right away... and many merchants don't accept it anyway... and it's easy to see why more people aren't using it.

But even in the face of such challenges, many people have become educated about Bitcoin over time and many people are slowly coming to see its advantages. Adoption is increasingly, slowly but surely. I really have a hard time viewing the state of things today as anything other than a success. I think we need to have more patience... people don't just suddenly adopt new monetary conventions over night.