I believe for a lot of people, meditation brings attention to anxious/traumatic thoughts. It's tough to move through that if you don't have the proper guide or tools. For these people, it could be more helpful to focus on more body centered, bottom up approaches that work with bodily sensations, rather than top down that focuses on cognition. Hiking and biking with noise cancelling earphones have been my go to...people don't think of this as meditation, but it's been great for me because the physical exertion prevents me from dissociating off into mental spirals.

Probably the same reason why talk therapy is not as effective for people diagnosed with ADHD. They need more body centered approaches.