The New York Times did a great pre-post-mortem of what happened—or what didn't happen—with the Ron Paul campaign:

Even Mr. Paul cannot entirely explain why the passion he generated, especially among young people and those his campaign identified as motivated supporters, did not translate into more votes.

I don’t have a full answer for that,” says Mr. Paul, who says he believes ballot irregularities have chipped into his numbers in some places. He adds, “I think there’s some problem with always making sure this energy is translated into getting to the polls.”

Though the campaign says it still has some tricks up its sleeve, it now faces a hurdle just to place Mr. Paul’s name in contention for the nomination: a Republican convention rule requiring a candidate to have the greatest number of delegates from each of at least five states.

Maybe it's Snakes on a Plane syndrome? Loud excitement on the internet doesn't always translate into real-life excitement. And as to the big crowds of people at Paul rallies around the country: You can find 2,000 people who are really into anything in a big city. If Reddit were to host a pro-Pedobear rally at Westlake Center next week, I bet you'd get more people than Ron Paul drew to Seatac a couple months ago. I anticipate lots of conspiracy theories to spread over the internet in the next few months, but I really don't think it's possible to rig fifty individual primaries. The support just isn't there for Ron Paul. The end.