>>3531655That's a great example, actually.
He was astoundingly good at what he did, but what he did isn't very interesting to most people. You show a Sargent to Joe Average who isn't particularly interested in art history or technique, and he'll go "eh, it's nice I guess". Even if they recognize how well executed things are, they just don't care all that much about portraits.
I believe that was even the primary criticism of his contemporaries; that his work, while expertly executed, was completely lacking in idea.