One point is that "the best available evidence" is of very poor quality, with known obvious confounds and mishandling of longitudinal data. (For example, Robert Larzelere argues that by the methods used, grounding children, and giving them therapy, also harms them: (https://link.springer.com/content/pdf/10.1186/1471-2431-10-1...) Another point is that parents may be well placed to know what is best for their children - better than "experts".