My theory, utterly unproven, is that Tesla's seeing a glut of 2012-2013 era cars moving on past their 50K mileage and getting sold, and that they want to encourage people in the market for a Tesla to buy new or buy CPO (more profit to Tesla) rather than buy from private seller. This is a surefire way to discourage people from buying from a private seller, seems to me. Oh, and yes, it's a completely ridiculous policy change on Tesla's part.
Wait a minute. I see this as their way to August the SuperCharger network:
1. Don't warranty their products after a short time (50,000 miles, or whatever).
2. Turn the value of the really old cars (2012-2013) into so little that they cost more to repair than to buy.
3. Force out of warranty low value cars into the third party repair market (because of the price points of vehicle value vs. repair cost). All parts are from salvage and third party sources, manufacturers, alternate suppliers.
4. Because of #3, cancel SuperCharger certification for those cars.
Bingo! SuperCharger For Life is dead. It's only SuperCharger until out of warranty repairs stack up so high you can't possibly keep up by using the in-dealer* network. This puts a cap on the SuperCharger network, so that they can decide to cancel it in the future (for new contracts).
Unfortunately, we still can't value Total Cost of Ownership unless always selling before warranty expires, because a healthy third party repair network hasn't been fully established yet, but thankfully it's on its way.
This opens up an opportunity to build out a nationwide third party SuperCharger network usage-charged for cars that aren't Tesla controlled and thus have no SuperCharger access. Right now there are only dozens of cars that would use it. In the future, it could be tens of thousands, and much further in the future, it could be hundreds of thousands, but by then, competition would be stiff and there wouldn't be much margin. Tesla wants to keep the 30% margins for itself.
A third party charging network could open up at the third party repair shops. They could wire large solar power arrays into large battery storage arrays that directly DC charge the Teslas at maximum DC charging speed.
They can recycle Tesla batteries, Tesla cars, Tesla parts, and use solar power to do it, and be "greener" than Tesla Mothership. I wonder what kind of government credits and support they could get for all of this recycling and environmentalism.
* If they're going to act more like a traditional car company, I feel OK using traditional car company terminology.