I think the problem comes from schools and universities. They force students to think in volume (6 pages, 12 pages) when writing. Who is a better writer: Julie, who wrote 12 pages of coherent paper or Mary, who stacked the same essence in 4 pages of superb writing?
According to the guys who teach -- Mary should receive about an F on her paper while Julie will get a B+.
There are many, many flaws with the school system. This is one of them. (The other problem is that there are a lot of people who think they're Marys when in reality they're just writing short, crappy essays.)
Honestly, I've only encountered this in CS writing classes (40 page minimum requirements docs, etc). All of the actual writing classes I took used the min. page requirement very loosely. The teachers/TA's explicitly said that writing well was much better than writing more.
According to the guys who teach -- Mary should receive about an F on her paper while Julie will get a B+.