They fall for all kinds of false representations of history (and economics).
When the Tea Party movement started out, they were angry at both parties for fiscal irresponsibility. The most fiscally irresponsible party in the past 50+ years, of course, has been the Republican Party. But the Tea Party leaders let themselves be bought out by Republican operatives and in some instances ceded leadership decisions to them. Now, they treat earmark kings and deficit spenders like Mitch McConnell as heroes.
The Tea Partiers are to the Republican Party what blacks are to the Democrats: they'll always be on board, providing votes, and getting lip service for all the things they demand, without any results.