Not sure why you're getting so hyperbolic. The point isn't to write as much as possible, it's to be able to get all of your points across. I'm not talking about where the "answer" is 10 words long, I was thinking of a general essay. Longer isn't better, however, half an essay may be pretty useless to get a good grade, and if you can write twice as fast, you have a much less chance of running out of time, for any quantity of "time" without having to allocate hours, wasting more proctor time and making exams harder to schedule. Because like someone else said, they don't impose a time limit to screw the slowest-writing students, they do it for practicality (my above comment was trying to explain that).