Answer:
The answer is: Although the payment is the same each month, the interest that accrues each month decreases.
Step-by-step explanation:
In an amortized loan, every time you make a payment you pay both interest and principal, so the next month the principal's balance decreases (even if only a small portion).
Then next month when interest is calculated for your payment, it will decrease since the principal's balance has decreased. So even if the monthly payment remains the same, a larger portion of it will go to reducing the principal.