Ultimately it's a business and shareholder's value matters.
Not really. That's not the only driving force here.
You and many on this thread seem to assume Apple are wizards, who can just build whatever they want and its purely profit motives (shareholder value) that limit them from building what
you want them to make. If this were true, Apple software would never have bugs, as that only hurts shareholder value by decreasing customer satisfaction, but obviously thats not true.
All technical businesses, and especially Apple, have to consider product decisions through 3 main lenses:
Is it
feasible? (can it technically be built etc.
engineering)
Is it
desirable? (do people want it, will they use it, buy it, etc.
design)
Is it
viable? (does it make money, create shareholder value etc.,
business)
Let's look at some examples
Airpower - it doesn't matter how many people they think will want it or how much shareholder value they think it will create, it was just not technically feasible.
Touch screens on Macs and macOS - this is a well known design decision. Apple leadership doesn't think it will actually be desirable, so they chose not to pursue the technical challenges even though they could be overcome and it might even help them sell more macs. You may disagree, but especially in the Windows 8 era looking at the lackluster competition, it seems they were correct and its actually not something people want and doesn't actually make the product more desirable. It turns out a really good laptop and a really good tablet are actually better than a 2 in 1.
RCS for iMessage - this is a business (and regulatory) issue. In this case, while its still a lot of effort, its known that Apple could solve this but chose not to for profit and other business motivations until regulatory bodies have now forced them to change, and so now they are and will implement a solution considering the other factors as well.
The idea of an iPhone being a "do everything" pocket device or dockable computer is much more like Airpower or touch screen macs, it's not like RCS iMessage.
There are significant technical and usability issues with this idea, (which is why the samsung Dex has not gained any kind of popularity btw) but yourself and many on this thread seem ignorant and convinced otherwise.
Its possible this could change in the future with advancing technology making the idea more feasible with less tradeoffs so therefore also more desirable. However, I don't think that will happen for many reasons, especially since our computing needs change over time and so it's a moving target.
And this would be an interesting conversation, but just repeating, "it's because apple wants to sell more stuff" is pretty ignorant and boring. I'll leave it at that.