I have seen their kiosks in almost every major supermarket for years.
(I know, this fact doesn't make the digital rental any cheaper...)
Either RedBox is losing money on each rental, or....
The world of physical rental - at least in the US, not commenting globally - can rely on the First Sale Doctrine, which dramatically alters the economics.
They can stop selling the retail copies with the code included. That would pinch off Redbox, but upset customers.
They could stop offering download codes and instead allow people to register their retail copy to the streaming service with a copy of their receipt. Again, not very consumer friendly, but Disney is big enough to possibly get away with it.
Can't Redbox just go to a store and buy the movie and put it in their boxes?
But they won't, because Disney is the 800 lb. gorilla that can get whatever it wants by beating its chest and charging...
...the lobbying and litigating costs to its colossumongous IP protection budget.