Why are there so few? GOP have 12. DNC have 6 total. Compare that to 26 debates for DNC candidates in 2008 and 21 for GOP candidates in both 2008 and 2012. Did the DNC just assumed Clinton is the nominee? Extremely poor choice and I think this is sending the wrong message that the public doesn't need to listen to candidates and reducing the chance of allowing the best candidates to bubble up. Looks like it might not work anyway with the way Sanders is gaining. 21 to 26 is too many, but 6? I would love to see other candidates having a voice.
There isn't much in it for Clinton if debates give primary challengers credibility. And, if Clinton won't participate in a debate, no one will care about it. Besides, 6 sounds like a decent amount to me. The Republicans need a lot just to give their bazillion candidates at least a minute of airtime each.
This. There's only 2 legit candidates in the Democratic Primary field right now. There's like 92 on the other side. 6 is more than enough to get their points across and even to give the lesser candidates an acceptable amount of air time.