Because you have an idea of what to expect, and even if you like the pros, the cons scare you.
You're afraid to get that close to someone and realize that you can't get physically close to someone without getting a little turned on. And you're afraid that you'll freak the other person out if they find out, embarrassing yourself. You'd rather save yourself the humiliation and simply stay on your own.
You're afraid to face another person in a way that you probably haven't yet. Despite how disconnected and far apart you feel physically and emotionally with others, you're afraid to do this with someone you don't know. But the idea of laying down and cuddling with someone is scary to you, especially since the idea is so foreign to you that it can't be exactly what people say it is. It must be something else.
You're afraid that it's almost like cheating on your significant other. You're not getting what you want out of your relationship for one reason or another (you both travel a lot, have different work schedules, there's been a breach in trust, etc.), but the idea of getting a service like this feels wrong for some reason even though it's a platonic, therapeutic service. So you stay on your own and let the issues with your spouse build up and continue to frustrate you.
You're afraid to be emotionally vulnerable. You have problems in life, like most people, and you're afraid to dig into them. It's much easier to numb yourself with being busy all the time, drinking, drugs, sex... it's so much easier to do it that way. Then you don't have to face those emotions head on.
Because you're afraid of what you'll find. Not in professional snuggling itself, but in yourself.