I don't buy this argument.
There has been nothing stopping other companies from releasing HyperCard-style tools for the Mac. And many have. But they have (as far as I'm aware) not dominated nor flourished particularly well.
What may have seemed amazing to a few people -- including me; I loved HyperCard as a kid! -- was possibly simply not the most valuable use of time, especially for a company trying to dig itself out of the hole Apple was in during the late 90s.
As far as "use" and "programming" being kept separate in modern computers:
1) I don't think this is something a company even as powerful as Apple can control. Third parties would fill in the gap if masses of people were clamoring for a HyperCard-like experience. And arguably they have. You're reading this in a web browser, right?
2) I just don't buy that we're in some digital dystopia with an Iron Curtain between "users" and "programmers." What you can do with a computer just with "use" and not "programming" is just insane compared to the 1990s. "Non-technical" people who need to get something done can find a wide range of powerful tools to do the job. No one needs to make a calculator from scratch. No one needs to make most of the software tools they need in the day-to-day from scratch. And, again, there are plenty of available tools that allow for light scripting to give "non-programmers" even more control. And of course there are professional programmers who can do things with computers that lay people cannot. This would be true regardless of the existence of HyperCard.