Why "sufficient cause" can be used either without "the" or "a"?

Context:

The letter has inflamed opinion in Iraq at a sensitive time in US-Iraq relations, amid difficult negotiations over retention of US bases in Iraq after the scheduled departure of US troops in December.

Iraqi officials said the new information was sufficient cause to deny the Americans any bases and demand all troops leave.

"The new report about this crime will have its impact on signing any new agreement," an Iraqi parliamentarian, Aliya Nusayif, told the AP. She said Iraq's parliament would investigate and seek to prosecute any US soldiers who commit crimes in Iraq in the future.

More:
http://www.guardian.co.uk/world/2011/sep/02/wikileaks-iraq-massacre-inquiry