Yes but if Universal did that they would then have to build a payment or subscription system into their app and spend a ton of money managing that and supporting it. Or are you suggesting they give their movies away for free on the app? If so then they're better off just letting the stores take a cut - that way they actually earn money.

If they were to give away their movies for free (if that's what you're suggesting) how - exactly - would they monetise that successfully? Unlike the music industry which can make up losses on record sales through concerts and merch their isn't really an equivalent for the movie industry.