Valve never wanted to be the leader in the handheld market. The wanted to show other vendors that it can be done and hoping they run with it, which they are. They just want to sell the software so they win no matter what. You’re not going to see a steam deck 2 anytime soon and I doubt you’ll ever see a steam deck 3.
They don’t offer a trade in program because they don’t sell used decks and you don’t need one.