Many students come into the FA office and wonder why they can't just fill out the necessary paperwork once and have it done. But as with many things in FA, things aren't that simple.
The main reason you have to reapply is because the foundation of your FA (you FAFSA) is based on income, and income may change from year to year. The FAFSA has to be filed every award year (the period between July 1 and June 30). Your Direct Stafford loan eligibility is dependent on your FAFSA results, so without a FAFSA, there are no Direct Stafford loans.
As far as Direct Stafford loans are concerned, some schools are able to allow students to sign a two-year prom note and some only allow a one-year prom note. Master Promissory Notes (MPNs) are only good for a certain amount of time before they have to be completed again. Some schools are only allowed to use one-year prom note, which means you'd have to complete new loan paperwork each year.
Another reason you have to complete new paperwork each year is because of of your Satisfactory Academic Progress (SAP) calculation. Colleges have to monitor your SAP and make sure that you are successfully completing the courses in a manner that is leading you to completion of your program with good enough grades and in a timely fashion. Most often, you should finish with no less than a C average and finish in no more than 150% of the program's published length (so for a 2 year program, no more than 3 years). When this calculation is completed depends on the school, but before you can take out your next year's FA, your calculation will have to be completed. If you are not meeting SAP, that may affect your FA eligibility.
Even though many students would rather just fill out their FA once, it's actually a good thing to stop into the FA office to refill out your paperwork. This way, you will become more familiar with your own FA and terminology. It's a great time and place to ask questions, and a great time to understand your situation.