Why do people eat fish healthier than meat?

Of course, eating fish is healthy and nutritious, especially deep-sea fish. As far as I know, fish meat has lower fat content and richer nutrition than red meat such as pork and beef. Fish is wool, and it can't be eaten well. It has a bad influence on joints, rheumatism and inflammation, so doctors often tell some patients not to eat fish, especially middle-aged and elderly people.