My husband needs to change jobs. He has recently become 100% disabled through an old military injury but wants to continue to work. With this new income, he does not necessarily need the income of his present job. He is in a miserable job he has hated for the past few years and it is getting worse now that he is disabled. It should not be that way, but it is.
Our question is this: He found a job he wants to apply for and it is making considerably less money but it is something he will enjoy doing. The application question: Why are you leaving your present job?" is stumping us. He can't just say "I hate my present job", or "My boss is a jerk". "Change of Pace" does not sound right either.

Basically he wants a job that will keep him working and active, but not the physical demands of his present job. It is less educationally demanding and they may wonder why a person with his degree is going to a less paying/lower profile job.

So what would be an appropriate answer to this without getting into all of this?

That's a toughie.

I would say "To expand my working knowledge in a new position that offers experiences my present position does not have." When questioned, he can say that he's been there for a long time and he feels that it's time to learn a new job. That makes it sound like he appreciated the old job, and that he's ready to devote himself to a new one.

"I am looking forward to finding a place of employment that is a better fit for me."

"I feel that my current position no longer fulfills my career and personal objectives."

Everyone knows that people are looking for a job because they are unhappy in their current position. The reason for asking this question is to allow people to shoot themselves in the foot - bring up disputes with their employer, bring up job performance problems or personality conflicts with other workers. These are the things that you don't want to tell a prospective employer because it tags you as "difficult."

My suggestion is to keep it simple - "Looking for new opportunities" "Looking for a better overall situation" and don't worry about it after that. View it as a matter of fact answer and let it go with out worrying about further explanation.