I was at one of the very first TEA Parties in downtown Chicago. It didn't fizzle out because of a tendency towards apathy and the difficulty in sustaining a high level of outrage. It was hijacked by the right-wing social agenda crowd and they killed it.
TEA stands for "Taxed Enough Already", and in the beginning of the movement that was what it was focused on. Too many taxes. That WAS the issue.
Then came the right-wing social agenda crowd injecting anti-abortion, anti-gay marriage, and several other topics that had NOTHING to do with taxes and big government.
The original TEA Party movement was LIBERTARIAN, not "conservative". They were very much for keeping the gov't out of people's lives -- including out of the bedroom and NOT enforcing any social agenda.
What happened to the TEA Party is the same thing that happened to the Reform Party. Remember when Pay Buchanan hijacked the 2000 Reform Party Convention in Long Beach, the police had to be called and the Convention settled by the courts? They showed success where the Christian right-wingers never could, so they got co-opted and died because their soul was sold.