Because that has problems. One of which I pontificated about here. Another of which is--
Some writers' best work is their miserable hackwork. At least, everyone else agrees that it is their best. Sometimes the writer himself agrees. (And when he doesn't, it's tragic.)
It seems that some writers feel bound by the duty to be Serious and Important and Significant. And as a result, their work is tedious, overwrought, laborious -- and quite possibly filled with Very Important Stuff that demonstrates that being a writer does not result in having profound insight into Life, the Universe and Everything. The world-building is clomping. The characters are personifications of principles, not people, and the plot is always being shoved aside.
But sometimes they have to hack something out to keep the wolf from the door. And because this is not serious stuff they are free as a birdie. You can have characters full of verve and excitement. You can have an actual plot and keep to it to keep the story moving. You can have a wild, wonderful, wacky world that is so outlandish that no one would raise the question, "Could it work?"
And if you think those are all pandering to the mob, you are a tragic figure, but you may still perpetrate some of your best work that way.