Here it is in black and white. The reason you want to have artistry as part of any piano study is because the whole point of any art form is the self expression part. Artistry is the basis for self expression and that self expression is what makes all the hours of practice possible. It's not drudgery when you feel like you are expressing yourself. Self expression and the artistry involved in it are fundamental reasons for practicing any art form.
Piano students are so laden with all of the "nuts and bolts" of playing that artistry is often left out. Even if a teacher has an artistic sensibility, the development of artistry in a piano student requires more than just "do it like this" or directing a student to play with more emotion. I teach in a way that develops how the wrist moves from the first lesson. Within the first month I point out how the student's tone is different depending on how they have moved their wrist. Use of the pedal also begins at the first lesson with the subsequent listening to changes in tone.
Listening is fundamental to artistry at the piano. Young students are almost always fascinated by what the sustain pedal does to the sound of the piano. Artur Rubenstein called the sustain pedal "the heart of the piano". It's that listening to the sound caused by the pedal, that a teacher can use to develop artistry. The wrist also causes changes in the sound of a piano and should be considered part of a students artistic development.
In piano study, the teen years are a real "line in the sand" for young piano students. I believe that more than 90% of adults who took lessons as kids don't play as adults. Somewhere along the way, they quit. When piano students arrive at the teen years, if the artistry hasn't been developed, there's only the hard work and kids are left to choose between a social life or hard work. It's easy for most kids to choose the social life. Thats essentially why kid's musical lives don't make it across the bridge to adulthood.
As a parent, you might be saying to yourself, "I'm not paying for lessons to have my child become a concert pianist. I don't care about all this artistry stuff." That's understandable, but hopefully, you are paying for lessons in order to achieve a lifetime of enjoyment for your child. Even if you are only interested in the brain development benefits of piano study, getting your child's self expression in addition is pretty fabulous.