Our understanding of psychology and the human brain changes so often that I'd have a hard time trusting a source that hasn't been recently updated.

Even with that said, the average time between DSM revisions is, what, every 15 years, give or take? I wouldn't exactly call that "often".

I can't trust the DSM because so many studies, experiments, and results regarding psychology and psychiatry simply cannot be reproduced or repeated with any degree of reliability.