Confused about the JFK Assassination

Hi guys. I am researching the JFK assasination. And can someone help me answer this question:

Both the Warren Commission and the HSCA agreed with the single bullet theory. The Warren Commission concluded that there was only 1 shooter and the HSCA concluded that there were 2 shooters. Both of the groups used the single bullet theory to justify their claims. Why does the Warren Commission get so much criticism for its single bullet theory and the HSCA does not get criticized?