[chrisseaton]

> but what is the core principle involved with not being paid for your work?

I doubt their core principle is to not be paid for their work, and they never said that it was - you've imagined that from a silly twist of what they've written. They said their core principle was to licence as CC.

Do you think charity volunteers have a core principle to work for free? Of course not - instead they have a core principle to contribute towards a cause and they accept not being paid for it in order to achieve that.

I would imagine this person's core principle is the same - they want to contribute their photographs for other people to use without licensing problems and they accept not being paid for it.