I don't know if it has always been this way but I find trying to coordinate anything with others of my age group (50 somethings) to be like herding cats. We complain about the milennials but my age cohort sure seems to want things on their terms and convenience and has the income to buy it. I also dive and it's such a pita trying to pin a group down without someone or another wanting to endlessly adjust because of some detail or another.
I wind up doing most things solo because.. I guess.. I want things my way too! But I like to think I'll stick with a plan whenever I do work with others.
I like the suggestion of sticking in countries you feel comfortable in with the caveat of also checking your own reasons for that. You want to stretch your comfort zone but not completely abandon it or you won't enjoy the trip.