There are some very good photo tour leaders (my opinion) whose trips do not fill up, and some I haven't heard of (of course, they may be great) whose trips are booked solid through 2025. Some of the difference lies in that mystery of mysteries, "marketing," plus the sometimes curious phenomenon of people getting attached to a particular leader and then going with that person over and over. On some of the trips I have gone on I am the only one who has not traveled with the leader at least once previously. I guess I tend to pick mainly on the basis of destination and scheduling (and to a lesser extent, cost), so I have little "brand loyalty," except to the guy who I think is the Dean of photo workshop leaders, Glenn Bartley. I know Steve is also excellent, and someday I would love to travel with him, but I have not so far.
Leaders can lose my loyalty by 1) showing unethical behavior in the field (based on my own values, of course; and 2) prioritizing getting his/her own photos over maximizing the experience for the paying clients. In a few cases a leader has kind of annoyed me because his own sense of what makes a "great" wildlife photo is different from mine. My son and I still joke about one leader's repeated exhortations to "Take the photo, they're fighting!" Birds or animals fighting (or taking down prey) are NOT my priorities.
In a few cases I have signed up for a workshop mainly because the price was so reasonable. Bargain hunting! I will not name names here, but in one instance this was almost a case of penny wise, pound foolish, as the leader was tolerable at best. Even so, I got to go to some terrific spots and I came home with great photos.
Doug Greenberg