It means the things we own right now.
I'm not sure what you are reading, but cars are not "thrown out" by their original owners. They are traded in, because they do still have a value. This trade-in process creates a secondary market in used cars that allows other people to purchase cars for a lower price than buying new.
If every person kept every car from the moment it first left the dealer until the car died, then there would be a lot fewer people who could afford a car. Basically, all those who can only afford used cars now would be priced out of the market.
Student or Learner