They lie. Since they only lease the movie from the distributor they can’t sell it to you, you only “own” it in so far as for as long as they’re allowed to store it on their servers they can show it to you. But the minute they aren’t allowed to have it on their servers you get nothing.
I bought Heavy Metal (1981) a couple of months ago. Amazon has since removed it for rent or purchase due to contract issues. I still own and can play the movie.