"In other words, we need to make it possible for people to build simple things without much coding. Oh wait, people already can build simple things, but....that's not what you mean?"
I think that the problem the OP has with most current app-in-a-can tools is that they don't allow users to create arbitrary simple things, but only fairly specific types of simple things.
The more generalized a tool is, the more special knowledge you need to use it for specific tasks. The advantage of stored-program computing is that we can take a general tool (a computer) and package it with a set of automated instructions (the stored program) to turn it into a specialized tool that you can use with general knowledge. That's pretty much the fundamental endeavor of the software profession.
Compilers, IDEs, etc. are themselves generalized tools to produce more specialized tools; as a result of being generalized, they require special knowledge to use. A programming environment that allowed you to create an arbitrary specialized application using only general knowledge of computing would certainly be a great thing to have -- in fact, I'd describe it as the holy grail of computing.
People have been pursuing that goal for decades. Partial solutions have been discovered in the past (the OP mentions Hypercard, Visual Basic, etc.) but have generally been insufficiently powerful. It is also frequently difficult to keep them up to date with changes in the underlying technology.
I think there's not nearly as much agreement on how a "web app" might look or work today as there was for a desktop app even as early as the early '90s.
For "classic" (content-based) web apps (forums, CMSes, blogs), there's already fairly sophisticated, end user-targeted tools that fill that role. For a lot of people, WordPress is the Visual Basic of the web. Some wiki engines could be said to resemble Hypercard.
But the community is so split on what the "modern web app" should look like (thin client? thick client? standards-based or not? use the DOM or draw directly?) that I think it'd be much harder to gain much support for a "Hypercard for the Web" -- many web developers, possibly even a majority, would consider it to be "doing it wrong" and "teaching bad habits" _no matter what it looked like_.
General purpose design tools are again the equivalent of DTP (and very welcome), but not an app solution (unless I have completely misunderstood the audience Macaw is for).
I think you're right. My problem with that problem is that it's some combination of naive, impractical and pie-in-the-sky. It'd be great for humanity if you didn't need any skills or training to make any kind of computing application you wanted.
While we're at it, let's also have a replicator to make any kind of food we want, instantly and deliciously, without any culinary training whatsoever, beyond being able to press the "pasta carbonara" setting (oh but I don't want there to be eggs in the carbonara, and can it have tuna instead of ham, and can it use a different kind of noodle, but I still want it to taste like carbonara and be delicious...)
We have shitloads of them. Squarespace, Blogger, Wordpress, on to new hotnesses like Macaw, Dreamweaver, on and on and on and on and on and on and on and on...it's really pretty insane to argue, in 2014, that we have some kind of lack of simple-to-use website-creation things.
If your response is, "Sure, but they can't do anything complex/building interactive experiences is still hard" well, we had Flash, etc, but also, at some point this is moving the goalposts so far as to constitute meaninglessness. If what you're asking is, "why isn't there a simple-to-use WYSIWYG editor that I can use to build anything I want," then my answer is, "it's riding on the back of my unicorn."
We aren't talking about sites (that would be the equivalent of DTP), but apps. Hypercard was used to author content, sure, but also create games, tools, and so on. I don't think that is moving the goalposts at all.
I think that the problem the OP has with most current app-in-a-can tools is that they don't allow users to create arbitrary simple things, but only fairly specific types of simple things.