- they don't know such a thing even exists
- they've heard stories about roleplaying which give the hobby a negative reputation
- they don't have time to get involved in another time-consuming hobby
- they feel that they lack the skills or imagination required to play well
- they know all about RPGs, but they just aren't interested
- they're interested but don't know how to get started
- they want to play, but don't have anyone else to play with
I'm not the only person who wishes more people would play RPGs. William J. Walton publishes a website and a podcast, both about roleplaying advocacy. He works hard to make the truth about RPGs known while dispelling myths. He sees RPGs as an educationally valuable experience in which all different types of people can and should participate.
I recommend visiting his website, The Escapist, and listening to his biweekly podcast, The Escapistcast. The amount of information Walton presents is astonishing. He seems to catch every mention of roleplaying in the news, and has a number of interesting projects he's working on for promoting the hobby.
If you love roleplaying and wish other people did too, head over to the Escapist and support Walton's work!