This is just about the only professional career I've heard of where people talk this way...
In my experience: Nearly all doctors will at least claim it as part of the reason. Many (most?) lawyers. Most teachers. Most academics. All social workers. The list goes on and on.In fact my first choice for counterexample would be your example - accountants. But in my experience they are often passionate about proving a helpful and necessary service, eve if they aren't passionate about the work itself.
For that matter, let's talk about a closer career to ours. How many people who are system administrators complain about relatives asking them for free consultations? Would that be an issue if they just loved configuring and troubleshooting computers so much? Even if you like computers a lot, what you get paid to do with them isn't necessarily fun.
-- From "Real Programmers Don't use Pascal", a classic in programmer's humor.
also, medicine, law, automotive engineers, pilots, merchant marine, musicians, actors... people are passionate about different things.
maybe you haven't heard people talk about their passions in those industries because you aren't in those industries?
what a bizarre thing to have to explain to someone.