Why do one thing all your life, when you might do different things, as many as you like, whenever you feel like it ?
It may be that this question is no more applicable to art than it is to any other area of life. Why be married and faithful when you might have any number of sexual partners? Why stay in one job when you might try others, or live in one place when you could move or go travelling ?
Such questions are crude, marked by exclusions and failure of empathy. They assume choice as a right and take consumption as the model for agency. They are also self-defeating, since, if choice is open, the decision for singleness or consistency will be as legitimate as any other.
No doubt mistrust of a single practice is the legacy of romantic notions of the freedom of the artist, of an effortless creativity, a constant self-invention. Investment in the idea of the artist as exception remains strong in a society where room for manoeuvre is still limited.
Why continue to make one form of art when you might develop or invent different practices at different times ? While such a question might begin in a genuine puzzlement, it would be unreasonable to press it beyond a certain point. Where art is concerned, interrogation should always be secondary to a genuine effort of understanding, to an attempt to inhabit the problems, to see a practice from the inside, with some sense of its advantages as well as its restrictions.