(You can still watch old movies of course, so if you restrict your downloading to old movies, and not fairly recent releases, your argument works.)
If we stopped making new movies, would people learn to appreciate older classical films they'd never considered before? Surely there have already been more movies produced than a person could consume in a single lifetime, though it's debatable whether or not most of them are worth viewing at all.
Once the medium platues (or long enough after to build up a supply), then this would work.
It's not like people are making professional-grade movies now in the free time, as they are now driving around cities with their own cars. Likewise, not everyone is trained to make movies as most adults are already trained to drive cars.
The argument being that art is intensely connected to the time in which it is created, and the function of art in the context of the progression of humanity requires that artists constantly make new art for the current generation.