The logic goes like:

• If you enjoy doing something, that's leisure, and you should be paying for it.
• If someone is paying you to do something, then it clearly isn't something you'd pay for doing yourself, so you can't enjoy doing it.
• Work is suffering, or it isn't "real" work.
• If you aren't suffering while claiming to be at work, then you're clearly stealing your employer's time.

Unfortunately, there do exist people willing to get paid for doing nothing, pretty much every employer ends up meeting some sooner or later, so even those who claim to look for people who "like and are passionate about their work", in reality end up trying to catch the lazy grifters to cut them out.