Why a test score?

So, I was talking to a school counselor about how little colleges look at GPAs compared to how much they look at test scores. So, my question for this week is: Why do the test scores mean more than the GPA?
So, I guess the first reason would be that almost anyone could get a 4.0 if they took classes like foods, seminary, and P.E. You can find classes that don't require any outside work. All you have to do is show up and listen, participate and etc. So that's probably one reason that GPAs aren't as reliable as test scores.
Secondly, I think that the students who are taking the classes that really require a lot of hard work might be the ones who aren't getting complete straight As. They are taking harder classes with SO much more work involved and get lower grades because...well...you know, only so much can be done before you take a history test. So the ones who are at higher levels might not be getting as good of grades as those who take the easiest levels. While good grades do show a desire to try, not so good grades don't mean that the person isn't smart or didn't try really hard in school.
Finally, the last reason that I can think of that a college would prefer to look at test scores would be because it tests your actual knowledge. While the ACT and SAT don't test all of your abilities, they get you pretty hard on the things that you are supposed to have learned in school. I do think that there are acceptions however. Some people freeze up on tests, it also may not be fair to test only one attribute (that of intellegence) rather than encompassing your ability to work hard, endure and be a respectful student who's willing to learn.
While I don't necessarily agree with seeing test scores above a GPA, I have been able to examine the points from where the schools are coming from. They want to know your actual applied knowledge ... not you. (Just Teasing).
Well, I decided to do this blog today because my weekend's FULL! It's the end of the school year and I think I'm going to do homework, run, more homework, and go to sleep. Love ya'll. Bye.