If there really is such a thing as a "trance" and that is a huge "if", imo, how could it not be a subject of psychological study?

I do not think it is obvious that such a thing exists or not - only because I have not studied it in any depth. I can easily imagine, though, that there are many 'facts' about trances and altered states of consciousness which are widely known and a lot less widely refuted.

It is not clear to me the extent to which Jung's work constitutes actual science.