There are 4 main things that colleges consider in your application, and they probably weigh them all about the same.

1. GPA and classload - what kind of classes did you take and how well did you do?
2. SAT/ACT score
3. Extra Curricular activities - what are your interests and how involved are you?
4. Essay - are you able to effectively communicate your ideas through writing?

The reason colleges think the SAT and ACt are so important is because it gives them a good basis on which to evaluate students. GPA and extracurriculars can vary depending on where you go to school, but the SAT can't. This is why it seems like the SAT and ACT are more importnat than they should be