This is an interesting question. The simplest way to answer this question is by saying no one is completely consistent. This is just a fact of life. So, Oscar Wilde may have said something and followed through on some occasions and at other times failed in his consistency.
Another possible answer is that people can have more than one reason for writing. So, a person can produce art for art's sake, but at other times have a meaning beyond this. This does not make a person inconsistent,but it makes a person multifaceted. In light of this, we must resist the temptation to view a person or a person's work through only one lens.