This is going to be long, but I think it’s necessary given that so many people ask for something that, if you know Apple’s philosophy and the history of the iPad, is clearly not going to happen.
First of all, many people forget that the iPad was born against the classic tablet PC concept, which was never a hit because it wasn’t a real tablet. Many people thought by that time that Apple was going to release a mac tablet, but they didn’t. Because a tablet is a device that does certain functions of phones and computers much better. It’s designed with a finger’s precision as base input, you can properly do everything with your finger (that’s important when people argue that the magic keyboard or the pencil prove anything), in a particular form factor.
When some comparisons are made between a MacBook Air and an iPad Pro at the same price level, they usually forget that browsing is a pleasure and provides much more direct UX on the iPad compared to the Mac. As with Photos, Books, Notes, etc. This is not only a checklist competition, some of us wouldn’t consider a MacBook because it doesn’t provide the experience of an iPad. The iPad can also do (besides doing many stuff better) things the MacBook can’t, like live analysis of the posture of a player or provide the best experience in drawing.
And macOS wouldn’t provide that great experience, because it’s an OS based on windows with small buttons, a bar on the top and an interface based on indirect manipulation designed for the mouse. Sorry for the Apple marketing language, but if you’ve tried Windows with touch, you can clearly feel the lack of the tablet magic. You also cannot switch to macOS depending on whether the MK is connected. First, that’s not instantaneous. But most importantly: what happens when you’re in a macOS app and detach the iPad? You can’t continue if there’s no equivalent in iPadOS? How is it handled if it exists? Do we disable touch support in macOS mode? That’s strange. Apart from that: partitions, API (camera works on iPad, not on other Macs?), duplicated versions... It just feels wrong to have two operating systems in one devices, sending the message that you don’t have a clear propuse in mind.
Another point is that Apple wants to sell you two devices instead of one. They probably want, but they would even prefer to sell one killer device that the competence couldn’t match. Apple is known to cannibalize many of its products. But, contrary to what you think, I don’t think Apple would sell tons of them — in fact, it would be just a slightly better device than the current tabletPCs that would sell slightly better (worse than the current iPad).
Then “at least give me the option”. Many other companies do, they throw every possible option they can. And that’s fine, but Apple isn’t like that, and something is only worth it if it provides a great experience. You know: installing a toggle, even if you hide it, is in the end allowing the option, it means you’re fine with that happening in one of your devices.
So what’s the solution? iPad is evolving in two ways: first, (underestimated here) creating new profesional use cases not possible with a traditional computer, like mentioned above. And the second, yes, bringing features and apps from macOS. And that’s the reason of Catalyst, SwiftUI... but making porting apps and adapting for touch easier is a totally different approach than throwing macOS. There are also some really difficult points, like multitasking. What do you exactly propose to improve multitasking in a touch environment. I can’t think how the current one could be improved. Maybe just things will never be optimal on an iPad (CAD?, Logic?)...
...that’s fine: a Mac is a better device for that. Let iPad be iPad and evolve in the iPad way.