There are plenty of activities I can enjoy, and some, quite a few of them in fact, are profitable.
Once you shoe-horn them into the power dynamic situation of a traditional job (with the bureaucracy that entails unless you're dealing with Actual People as opposed to corporations), suddenly a lot of the luster disappears.
As a ridiculous example - I enjoy reading. It's not really work at all, right?
Ask me to read 9am-5pm and I'd start to find it frustrating. Or add in a commute, or very low pay.
The actual job itself is very rarely the issue for me. It's what you miss out on, and also the fact that it invariably involves submission, acceptance of being subordinate, etc.
edit: To be clear here; I'm not talking about work ethic in the sense of 'pushing through something you find difficult'.
More the general idea of not wanting to be a part of a machine, a construct that you don't agree with. Large corporations and their 'policy documents', for example. I don't want to work for a company in which my boss doesn't have the autonomy to speak to me as a human being - this stands regardless of whether my job is backbreaking labour or eating chocolate bars.