From a Clinton campaign email list:

The Iowa caucus  process  is a broken and flawed process. It was designed to allow for the active party Dems generally known to one another to assign delegates and was not designed to handle a flood of students and independents. It was a system designed to give more power to Dem party loyalists. In the tension over whether the candidates should be chosen by the party or by the general public, the Iowa caucus was designed to give the party the advantage. For this reason, the Iowa system failed on Thursday.

Translation: we couldn't control it. So it sucks.