Why was my case dropped?

[cortarm97]

I am from California. I was stabbed by an acquaintance during an argument. The argument was about owing money, and the altercation was not physical. It was one stab to my abdomen, that cut my liver, diaphragm, and my lung, and left me with 2 surgeries, and `16 days in the hospital, multiple days in the ICU specifically. The attacker called the police on himself and admitted to stabbing me. The cops interviewed me, him, and the two witnesses, who were his girlfriend and her friend. My story was I was stabbed out of him being angry, he said however that I "came after him" and it was self defense, his girlfriend also agreed to his story, of course. The other witness told a different story than both of ours, and I do not know what it was. Also I forgot to note, that the stories of the two witnesses were changed after they had a day to think about it. He was arrested and charged with assault with a deadly weapon. The officers took pictures of my knuckles and they showed no signs of assault, as well as pictures of the attacker, who also had no physical signs of assault on him. But he was released within 24 hours and the charges were dropped. The district attorney claimed that "there was not enough evidence based on the stories to prove to the jury he did not act in self defense" I feel like this is unfair for it to be dropped so easily, as there was no physical damage, and he was the only one with a weapon. How could he have any justifiable reason to stab me, if there wasn't even evidence of me touching him? If I am wrong please let me know without any name calling or any attack on my intelligence, i'm just honestly confused how a serious incident could happen and the charges dismissed so easily. Also does this mean I could just stab him for no reason and have my girlfriend say it was self defense and i'll be released as well? obviously i wont do that, but im just showing how silly it sounds

 

[Zigner]

Question: "Why was my case dropped?"
Answer: "there was not enough evidence based on the stories to prove to the jury he did not act in self defense"

ALL of the witnesses tell differing stories.