How can Rishis lose control and curse if they are enlightened?
Now, why did the Rishis (Seers) get angry and curse, I don't know. Usually not every Rishi does this. There were only a couple of them who did this. But every time they cursed, something great happened from their curse as well. That is why it is said, the anger of the enlightened also, does something good for the society, whereas even the love of an ignorant person does some harm.
A wise man's anger also is beneficial. He cannot do any harm, he only does good to the society.
So every time a Rishi cursed, it turned out to be a very big boon to the population.