Interestingly that seems to be a result of the CDC's own political leanings. They seemed to pursue the research with an explicit political goal, rather than research the effects of gun violence, and then find a goal[1]. Further, the Dickey amendment doesn't actually force the CDC to avoid researching the issue but rather preventing it from using federal money . to promote gun control:
"none of the funds made available for injury prevention and control at the Centers for Disease Control and Prevention (CDC) may be used to advocate or promote gun control"[2]
[1]https://www.politico.com/agenda/story/2015/12/why-we-cant-tr... [2]https://en.wikipedia.org/wiki/Dickey_Amendment_(1996)