It could perhaps also be that it would work without the trip for some people, for example if the depression was more like metabolic/chemical or something in nat

It could perhaps also be that it would work without the trip for some people, for example if the depression was more like metabolic/chemical or something in nature, while for other people the depression was caused by their life situation or other issues and working through it through a trip would help. So basically like antidepressants and psychotherapy, both work but some people get more out of one or the other.