They've "thrived" because of what I just said - Disney has a near monopoly on blockbuster movies that come through theatres, but that doesn't mean it's good content people want to watch, they just don't give anyone much of an option.
I don't think their model would work if they just dumped all their content on Netflix. If it's not working with Disney+, why would it work in another service that's the same thing with a different name? People have plenty of options of content to stream that aren't from Disney, so their status doesn't mean anything in that space.
Also it's not "great partnerships," it's monopolistic purchases that allowed them to buy their way to their current position. And even with the well-beloved IPs they acquired, they still manage to fumble things. Look how badly they messed up that Star Wars trilogy. They're not good at making content.
I don't think their model would work if they just dumped all their content on Netflix. If it's not working with Disney+, why would it work in another service that's the same thing with a different name? People have plenty of options of content to stream that aren't from Disney, so their status doesn't mean anything in that space.
Also it's not "great partnerships," it's monopolistic purchases that allowed them to buy their way to their current position. And even with the well-beloved IPs they acquired, they still manage to fumble things. Look how badly they messed up that Star Wars trilogy. They're not good at making content.