Released 15 months later. More like a beta feature in OS X from ~2006. Apple could make it work if they really wanted to. They don’t want to. Simple as that.I'm fully convinced the stages of grief are at play here. There's denial. "Of course the A12X is powerful enough to run it. See that demo? That iPad running four tiny apps that use hardly any memory work on SM!." There's the bargaining phase with, "if only Apple would limit the feature to 4 apps at once or ditch the second monitor".
Yet, no one bats an eye when Apple limits features annually on their iPhones only to their latest model. At least with the iPad, they limited it to four year old hardware. I suspect the reason is in the release cycle. iOS and iPadOS are always released at the same time with the brand new iPhones, typically on the Monday four days before their new iPhones arrive. So it's expected to limit features. It's new hardware, after all. Why release hardware if there aren't any new features?
iPadOS doesn't release at the same time as iPads, so there is always time between iPad releases and new features. Because Stage Manager was released 15 months after the M1 iPads, why shouldn't it work on 2020 or 2018 iPads? If they had released the feature in March 2021 right alongside the brand new release of the M1 iPads, would the reaction have been the same? Or would people automatically accept the limitation as hardware related, just as iPhone features are every single year? I suspect Apple waited until 2022 to release the feature because 2021 was consumed by Universal Control, another difficult-to-implement feature, and they didn't have the resources to do both. Or they didn't want two headline features.
The beta of stage manager as it’s called today in OS X from 2006 actually worked in a better way. The app in focus had all of its available windows on the right side of the screen available for quick selection and not ducked under other windows on the left.