"The film is no longer in the cinema."
Not at the first-run cinemas, but you forget all the second-strings like cinema cafes, airlines, prisons, hospitals, etc. All of these locations will pay good dollar to host content that's not available elsewhere at this time. And remember, this is all for view-once venues. The distributors won't go for one-and-done sales (videos) until they exhaust the oppotunity for view-onces since they still stand the chance of getting a double-dip until then. Which means they won't release discs until it has its day with On Demand/Pay Per View, either. Besides, for them, video release day acts as a second wind when it comes to advertising, so they're not too worried about people not remembering the movie.
"For decades bands have had merch stalls at concerts so you can buy CDs, tee shirts and other memorabilia."
Barring a phenomenon franchise like Harry Potter or The Hunger Games, loyalty for any one movie tends to pass over time. People go on to the next one. To movie companies, once the movie goes out on home video, that's about it as far as they're concerned. People will buy it or not at their choosing, and time usually won't affect the sales that much, as people who want the movie will be willing to wait (ask any diehard Apple fan).