It has nothing to do with want.
It was a poorly done study that purposely used a non representative sample you want it to be true so you ignore the flaws
And the CDC can and does study gun violence you just want to believe it can't but again you are wrong
Actually, if anything, it probably understated the problem.
There are 32,000 gun deaths a year, but only 200 of those are "Justifiable homicides by civilians'. The rest are suicides, accidents, homicides, and police shootings. (And given what we are finding out about police shootings these days, it's less likely we can assume they are all justified).
"YOu can study something, just don't say something the NRA won't like" is not letting you study something.