At the core of professional and personal development there are only two problems, how you work with yourself and how you work with other people. Because we are all unique and highly individual in terms of what shaped and shapes the way we work, there are as many ways of addressing these two problems as there are people who have them.
This requires the coach, trainer or facilitator to have an attitude of skilled curiosity in order to always keep looking for what will work in a new situation; and the humility to know that what worked in the past may well not work now or in the future. That uncertainty is what is so often intolerable to practioners and clients alike.
When the customer often wants neat, guaranteed solutions, and the providers of services want repeatable, scalable and profitable solutions, I can understand why the 'one size fits all' solution is popular, if flawed.