You've captured the youth vote in practically every contest, while losing among the older set and among hardcore Republican voters. In short, the demographic you do best in winning over is the least likely to be able to vote in a closed Republican primary. I would estimate that roughly two thirds to three quarters of your constituency is outside the ranks of the GOP.
A lot of my readers are big fans of yours: on those rare but pungent occasions when I have criticized you, I've gotten lots of "blowback" in the comments section and in emails sent directly to my inbox. Whenever I praised you, I've enjoyed a veritable avalanche of favorable feedback. I can't tell you how many conversations I've had with non-libertarians who praise you to the skies. Many people beyond the narrow confines of the libertarian movement are watching your campaign with great interest, and rooting for you – especially those who are concerned about our foreign policy of perpetual war. A lot of these people are not actually registered Republicans – although some have registered just to be able to vote for you – and that appears to be part of the problem.