To be fair, I think schools encourage this sort of behavior. I've had countless "$x number of words/pages, minimum" writing assignments. Eventually, you start to be convinced that every teacher wants it that way.
The more you write, the better you get. Your first ten thousand pages are going to be shit anyway, so better get them out of your system before you start publishing. For the sake of your editor, if not for the sake of your readers.
One of my favorite professors assigned papers with maximums. The maximum was a hard stop. If your paper was longer, she tore off the overage and graded the paper as it was.
My better professors had, rather than just minimums, either ranges or maximums.