Some realms of art still entertain this definition for art, but you are correct in that the vast majority of modern art is exactly this distinct departure from the notion that one must have an audience. Modern art came about because of the rise of the bourgeoisie, meaning, people of different classes could commission works, artists had more freedom in what they chose to depict, sell, create, etc, instead of being limited to being commissioned by the church or by nobility.
But you are getting into a debate that hasn't really been resolved in modern art either, this has been a debate in the concept of kitsch and collage, dada, Greenberg, photography, etc.
If you want to dance around the question linguistically, that's all fine and good, but there are people in the world who believe that art must be sold and there are people in the world who find value in it other than the fact that it sells. You've got the past and the contemporary interpretations of art conflated with the trends of culture. Plus, these circles weave and web together, people derive influence and inspiration from all sorts of places, art comes to mean different things depending on who is listening, who is speaking/painting/etc.
I mean, there is obviously either a rigid definition for Art which has no form in language and is thus inexpressible for all eternity despite the various shapes it may manifest as, or art is something else. No, just kidding, I have no idea what I'm patring on about.