First, it tried too hard to incorporate Democrats as identify itself as "not" a Republican group. No one ever believed this on either side, but this led the organizations to strongly de-emphasize social issues and thought that it could ween Dems away purely on economic issues. This was just bad judgment.
But something that the Tea Party could not do anything about was its age. In every meeting I went to over the course of there years, the average age was about 50. There was never a sufficient number of young, energetic people to keep the movement's momentum going.
I started to see the numbers fall fairly significantly in the talks I was giving in 2011, even with a presidential election on the horizon.
Today, I've been talking to a few, but more important I've been trying to arrange a national film tour for my movie, so I thought I'd contact the Tea Parties. State by state, list by list, the groups I've contacted are defunct, or their leaders tell me they only have a very small number of people. One big Dayton area group I spoke to, which had over 100 in attendance in 2010, had half that a year later, and now the leader tells me that he's lucky to get 30. The only issue, he said, that drew people out was "Common Core." Even then, there still are no young people associated with the movement.
So while the Establishment has definitely opposed the Tea Party and sought its demise, the Tea Party did quite enough to bury itself.