My tupence worth:
Art is an expression of a moment captured, real or imagined. For others to enjoy, yes, but also for the the artist. It is a product of something the artist just 'had' to do. Its a feeling or emotion expressed. When the viewer 'gets' it - they get that feeling also.
As for a reward for their work - is low down priority, reward so as to live to produce more is the aim.
A slightly cheaper quote, not always accurate though, is to paraphrase Andy Warhol (I think);
'Art is whatever you can get away with'