They could, but unless you get some legislature behind this, who is going to enforce it when they explicitly choose not to include it in the TOS?

Amazon cannot just let you download the content. It's not up to them.

It certainly is up to them. They negotiated a contract with the content producers that did not allow for that, and could have negotiated a different contract that did by offering more.

They could have, but they didn't. Unless you make negotiating such contracts illegal, they and their competitors & partners will keep doing it.

If they didn't want to continue serving the film until the heat death of the universe, then that's what they should have done differently, rather than just unilaterally screwing over all the buyers.