"they want their to be appreciated, so they expect pieces to be sold" is a clever trick but one is not related to the other. One could want their art to be appreciated and never sell it, but virtually no one would see this art for a variety of reasons including the fact that marketability increases visibility and that there is very, very little amateur art that is worth looking at, much less promoting to a larger audience.
It seems you agree that in fact art (that anyone sees) is overwhelmingly made to be sold.
I didn't say anything about their "main motivation" and neither you nor I (nor even the artist, frankly) could say much about what someone's main motivation is.
What we can say is that nearly all of the art anyone sees was in fact made to be sold, which is the specific claim that I made.