The simple reason why the DNC wants to limit the number of debates.

[octoberlib]

31. HuffPost has an article on it, quoting Communications Director Mo Elleithee

WASHINGTON -- Democrats announced Tuesday that they plan to hold six official debates between Democratic candidates seeking the presidential nomination in 2016.

Beginning later this fall, each of the debates will be held in one of four early primary and caucus states: Iowa, New Hampshire, Nevada and South Carolina.

Any candidate who decides to participate in the debate process must agree to do so exclusively, making them ineligible to participate in any debates organized by third-party groups. If candidates deviate from this rule, they lose the ability to take part in any remaining debates hosted by the Democratic Party.

A senior adviser to one 2016 campaign told The Huffington Post that the exclusivity clause came as a "complete shock." Officials from the DNC, the adviser said, had assured all likely Democratic presidential campaigns when negotiations over the debate schedule began months ago that no such clause would be used. The adviser further argued that holding only six debates would be disadvantageous to candidates who have relatively low name-recognition across the country.

DNC Communications Director Mo Elleithee acknowledged that the clause wasn't a part of the early negotiation process, but maintained that all options were left on the table. He further argued that voters would ultimately be best served by a controlled debate schedule.

"We wanted to have a manageable number that would still allow for real debates but that was a little more manageable than in past years, and we were going to explore different options and we left everything on the table," Elleithee said. "And so when you’re doing something like this, when you’re trying to coordinate something like this, yeah, not everyone’s going to love the outcome."

http://www.huffingtonpost.com/2015/05/05/democrats-presidential-debates_n_7214218.html