Note that not all Arts are "useful" and not all Arts are "Writings".
Most art is not intended to be an open-ended product to be further collaborated upon and extended in order to drive progress.
Protections are purely so that the creators can get paid in some shape. There is still art if they don't get paid.
Copyright somewhat stifles that activity in art which consists of imitation; imitate too closely and you invite accusations of infringement.
A work of art being copyrighted is not what motivates and encourages activity revolving around copying that work's style. That's what it would mean for the work to promote Art as such: the work gets studied and it style becomes part of the artistic vocabulary. This will happen copyright or not; the only difference is the conditions for compensation.