What is the point of getting braces if your teeth don’t stay straight after they come off??? 😡

I had braces about 10 years ago and have had a permanent retainer on the top and bottom since they came off. About 2 weeks ago my top retainer broke so the orthodontist decided to just take it off and give me a retainer to wear at night. It took 1 week for the night retainer to be ready and in that one short week my teeth have already started shifting! I’m so freaking frustrated and can’t understand why they can’t just stay straight after all these years.