Yep we do know why, in a word: Gerrymandering.
You people won the House, super majority in the Senate, and the White House in 2008. Just how did the GOP gerrymander the country barely 2 years later when the American people obliterated the Dem's in an historic loss of the House?
You people refuse to accept that your policies and agenda were rejected. You have 101 far fetched excuses for your loss, none of them true.
That's easily explained and as easy as a Poli Sci 101 blue book midterm question.
The power elite used money and fear based demagoguery on this single word "Socialism", to create fear in the general public.
In doing so the R's created a grass roots movement attacking the Obama Administration and all Democrats as anti capitalists, whose hidden agenda was to remake America into a People's Republic.
Conservative radio was complicit in this theme and by using lies, half-truths, rumors, innuendos, and by cherry picking phrases from the speeches of Obama and Pelosi, created the sea change based on distortions which created the fear and mobilized the biddable.
Demagoguery by Republican Pols upset that they lost the white House, and that an African American man was in the White House fanned the flames of bigotry, attacking The President as a foreign born
Manchurian plant and not a real American.
Racism, already out of the closet when Mr. Obama was nominated by the Democratic Party, really got going when he was elected, and when he and the D's sought to reform health care, the R's and bigots came together on a single cause, make Obama a one term President.