The only reason why I chose Lindsey Graham for my example, was that he's stuck in JV debates, and had I could articulate a reason for his candidacy -- as opposed to Bobby Jindal, Rick Santorum, or George Pataki. I honestly can't figure out why their staying the race, except for perhaps for personal marketing reasons.
Lessig seems to think that if he eked his way onto the stage of a televised Democratic debate, he'd have a chance of jump-starting a national political campaign on the issue of campaign finance.
But it's actually the reverse: you only get onto a debate stage if you already have a campaign. The polling criteria is not a gotcha. It's just the easiest way to ensure that only people with actual popular traction get stage time. The debate is not intended to be a "big intro" opportunity. There are other events for that, like the convention (Obama), or big events like the Prayer Breakfast (Ben Carson).
In part the difference in the numbers between the parties is simply that there is no clear favorite on the GOP side, while there is an overwhelming favorite on the Dem side. There are a lot of senior Democrats who have chosen to sit this one out rather than challenge Hillary.
I guess that's the difference between the Democratic party debates and the Republican party debates. I know that sounds like a troll, but it's not. The GOP primary debates had 17 people running, the Democratic primary had 5 (not counting Lessig). No one seriously thinks that Lindsey Graham is going to be the nominee, nor did anyone think that he could be the nominee when he ran. He's a single issue candidate (national security) and his agenda is make sure this issue is discussed during the primaries. The same thing with Santorum and Huckabee ("traditional values"). It's not a new phenomenon. Back in 1988, Pat Robertson ran with a "Christian conservative" agenda, but no one seriously thought that he was going to be president. His role was to highlight the power of the conservative evangelical Christians in the Republican party, thus causing the eventual nominee to (and the party as a whole) to pay attention to their issues. There's nothing with this tactic, and it may even be effective. But it seems like it's more prominent on the national stage in the Republican Party than the Democratic Party.