From my prespective, I would put money as the first reason, particularly when personal circumstances change such a job loss or other situations that suddenly require that resources being allocated for other purposes.
That’s what I would do myself. If I were in a financial crunch, I would immediately look at all my expenses and eliminate all beyond the essentials. Personal training would be on the chopping block with others. It is not that it could not be re-instated later when things change for the better.
As the others have stated: results and money.
From a results stand point it could be both results achieved or a lack of having achieved results.
A third reason that I’ve seen a lot of recently is moving due to a job. With the economy being what it is, a lot of people have had to change jobs or more altogether to get a new job. The trainer they were seeing may not be close to their job or home any longer.
Money, time, and results. I try and turn over my clients ASAP by getting them to their goals or forging a doable path for them to complete on their own. I feel that once (most) my clients are really in the swing of things its time to cut the leash and let them try and fly solo. Normally they keep the results coming on their own and this lets the cost of their training be more manageble without me having to formulate some kind of “special deal” (which almost always costs you money.)