Ancestry is getting out of the yDNA and mtDNA testing. They plan to destroy the saliva samples. My question: Why can't they retain the samples? Even if they choose not to release them, what is the logic for at least retaining them? We could order autosomal tests from them in that case.

It's a hardship for the families who have lost loved ones and for whom the saliva samples are irreplaceable. Ancestry could mitigate the loss by at least holding onto the samples and allowing those of us who had ordered the testing in the first place (hence owner of the samples) to order autosomal tests from them.

And, who knows? There could in that case be some possible reevaluation as to whether they might even return the samples to us, who had ordered, paid for, and owned the samples and data in the first place? FTDNA does allow for beneficiaries to order new tests, so why wouldn't Ancestry at least consider the concept of beneficiaries? (That might facilitate the return of DNA samples to the families?)
And who knows, maybe Ancestry might return to the yDNA business at some future time? In which case it might have been productive had they had held onto the current samples and data?

Or if not, it would have been thoughtful of Ancestry at least to have a holding period during which time they might agree to test the same data points that FTDNA does, so that we could at least have some meaningful data points to transfer over to Ancestry. The data points that Ancestry tested just aren't meaningful for transfer.