My guess would be offloading storage space while adding monetization revenue.
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I doubt they're deleting the master copies or the master renders or anything, so the only thing that would be offloaded would be the "consumer" renders. A Blu-ray movie with no additional compression added is between 15-40 gigs.
A consumer like me has a 300 terabyte storage array, presumably Warner Bros has even more than that (and certainly could afford more than that), so it feels like 40 gigs per movie is basically nothing.