Hmm...seeing as how ACOTE now requires you to have one fieldwork that is mental health focused, I can't imagine there are programs that don't teach a Mental Health class at all. My program does in our second year, but in first year during Neuro, we also talked about it, and it was touched on in other classes as well. And no, you are not wrong; OT was founded in mental health practices, and part of the Centennial Vision that AOTA has set out is to get back to this.
To add, the ACOTE standard does not mean that you have to be at a mental health facility, but that the focus of that fieldwork placement will be on the mental health aspects of the client's treatment. Unfortunately, there aren't as many OT jobs in dedicated mental health facilities as there are other places, due to funding, etc. Hopefully that will change in the coming years.