Why and/or how can a hospital or its doctors get away with not providing professional basic care?

My father was in a motorcycle accident. He was air-lifted as a trauma to a trauma hospital. There was no x-rays taken. They tried to release my father, but he was not able to walk. So they provided him a walker and release him the next day. My father suffered a seizure on the way home, I was got him to another hospital where he was revived and found that his left side was broken and had to be sent to another trauma hospital due to the severity of his injuries which also included a broken back and brain bruising. My father has passed due to a seizure suffered at home and was unable to be revived. My family wants to know why the first hospital didn't provide care. I understand I can not prove the hospital caused my father's seizure but they shouldn't be able to treat people they way they treated him.