I think a far simpler explanation is not that control to the ability to program has been intentionally deprived from users, but rather that the vast majority of users have no wish to have such a tool, and that Steve Jobs recognized this.
I think that some proof of this exists: Excel, Visual Basic (and its formbuilder), Applescript, Autohotkey, etc all exist.
Those tools are all intentionally approachable, as was hypercard, and yet the vast majority of iphone users would not wish to deal with those tools or ecosystems. They would much prefer a company do something called "software development" and give them a working specialized application.
It seems more likely to me that Hypercard was eventually seen as a dead-end, not as a threat to the existence of selling apple software. Sure, you could spend significant effort on building a tool that is powerful for novice users (letting beginners create basic automation and forms easily), but less powerful for experts (providing less powerful design, abstraction, and programming features than more typical programming languages).