It's easy to point to 2010 and say the problem is that the Left just didn't bother to show up ..so they have only themselves to blame, but I don't buy it...and I never will. We showed up. But the Right was being driven into a mad frenzy with talk of a black usurper in the White House. The airwaves at the time were turbulent with the vicious rhetoric of "Death Panels" and "..one-sixth of our economy being hijacked by the Muslim President." There was an astroturf movement funded by right-wing billionaires to neutralize the 44th President and everything he attempted to do. The media manipulation jumped to a new level of virulence. And the mobilization of Republican voters was part of the program. Hate and fear ramped up the participation of voters on the Right.
But the biggest reason that Republicans took control in 2010 was the manipulation of the election through electronic voting. The corporations that made these machines called their software they 'proprietary'... which disallowed scrutiny of the source code at the heart of the systems. I recall more than a few close contest being decided by large numbers of votes for the Republican that were 'found' on a poll worker's laptop in the wee hours of ballot counting.
The disregard for the will of the people has been a trademark of the Right for decades. They are never only working one con at a time.
You can say that overall voter participation is appallingly low in this country, and I would agree. But plenty of us did show up in 2010.