Tesla don’t want you to transfer FSD because the people that bought it under the original product description represent a massive liability in the event that FSD never works as well as originally projected.
With things as they are that list of customers and associated liability will eventually disappear.
This is a good point if it's handled as a "transfer" under the now obsolete language of those original purchase agreements (here accepting for argument's sake that said language is indeed the liability that people claim it is).
But, why does it have to be handled as a transfer? It could be structured simply as an incentive offer
to trade in the old Tesla and get significant or even full credit towards the FSD Capability option on a new Tesla.
By doing that, they give owners what many have been asking for, they removed the perverse disincentive for buying a new Tesla, and they successfully retire the vehicle that (t's argued) has the liability risk associated with the undelivered feature. Also in this incentive structure, they don't have to concede that there is actually any implied liability - it simply becomes a non-issue. There can be a bit of fine print in the offer acceptance, where the owner of the trade-in vehicle effectively abandons any such claim, but without Tesla implying that there would have been any under any circumstance.
It seems to me that structuring it this way is a win for everyone. I can't say that there wouldn't be a few diehard OG owners who just want to get into court with Tesla, and would turn down even a good incentive just to hang on to their perceived legal trump card. But I think that would become a very small number, and their position is already dubious even before this proposed solution.