Why has the price been dropping so dramatically over the past few years???

I was on Facebook Marketplace looking around for stuff I don’t need and cars I can’t afford, and I saw a couple Mustang GT’s listed for between 3-4 thousand. AND THEY WERE SO SO SO CLEAN!!! I remember checking the market price for my car when I first got it, and it was 5-7 thousand for a clean one. What is happening 😭