Same reason a study with positive outcomes about coffee/alcohol/gay parenthood/gender reassignment/<insert issue> are not criticized as much as a study on the same topic that had negative outcomes. We want certain things to be true so we (consciously or not) avoid criticizing studies bolstering what we want to be true and harshly criticize studies we want to be false.
I like to think science always prevails in the end (like with tobacco), but it can take half a century or more to converge on the truth.
Same reason a study with positive outcomes about coffee/alcohol/gay parenthood/gender reassignment/<insert issue> are not criticized as much as a study on the same topic that had negative outcomes. We want certain things to be true so we (consciously or not) avoid criticizing studies bolstering what we want to be true and harshly criticize studies we want to be false.
I like to think science always prevails in the end (like with tobacco), but it can take half a century or more to converge on the truth.