WarnerMedia stunned Hollywood this past week when it announced that its entire 17-film slate will debut on streaming service HBO Max the same day the films arrive in theaters, blowing up decades of lucrative "windowing" in the movie business. Those day-and-date releases include some hotly anticipated projects, like the latest version of sci-fi classic Dune, another Matrix sequel, Wonder Woman 1984 (technically announced earlier, and for Christmas Day this year), Godzilla vs. Kong, Lin-Manuel Miranda's In the Heights,  Clint Eastwood and Denzel Washington projects, and much else. I explain why WarnerMedia and owner AT&T likely had little choice, and why other studios likely will follow suit. It should make for a very good time for streaming subscribers, but a much less good time for movie theaters, and for many who make those movies.