I know what you mean. My sister is in excess of 100 lbs overweight. She is seeing weightloss success from many members in our family, but still resists...her excuse, of course, is "I can't afford it". Yet, as you guessed, she spends money on everything else (vacations, food, Walmart).
It's obvious to me that her "I can't afford it" is not her real excuse, but it's the easier one for her to say. It's harder for her to say "I'm scared; what if it doesn't work for me; I will continue to be the failure that I already am" (Of course, she never actually said that, but I bet that's where her mind is).
In most cases, it's just an easy excuse. The prospect is not ready for it yet.
