Most trained coach practitioners don't cite coaching as their sole source of income: According to the 2012 ICF Global Coaching Study, 94 percent of coaches indcated that they offer one or more services in addition to coaching within their professional practices. Examples of other services offered included consulting, training, facilitation, mentoring, teaching and counseling. (On average, we found that coaches offer almost 3 services in addition to coaching). Additionally, many coaches supplement their income with paid speaking engagements and by nurturing passive income streams.
To help coaches at all stages of their careers build their coaching businesses, in 2014 we launched our virtual Business Development Series. Our 2016 BDS will get underway in February; you can learn more about this offering here.
Additionally, it is true that not everyone who completes coach training chooses to practice part- or full-time: In some cases, they may find that they get the highest ROI by applying their coaching skills to their existing work (managing or leading a team, for example). In others, they discover through the training process that a coaching career isn't the right fit. This is why we strongly encourage prospective coaches to spend time in self-reflection before choosing a coach-training program. (You can find some good questions for self-reflection, along with details about coach training, becoming an ICF Member, etc., here.)