The reason for this is that HyperCard is an echo of a different world. One where the distinction between the “use” and “programming” of a computer has been weakened and awaits near-total erasure. A world where the personal computer is a mind-amplifier, and not merely an expensive video telephone. A world in which Apple’s walled garden aesthetic has no place.
What you may not know is that Steve Jobs killed far greater things than HyperCard. He was almost certainly behind the death of SK8. And the Lisp Machine version of the Newton. And we may never learn what else. And Mr. Jobs had a perfectly logical reason to prune the Apple tree thus. He returned the company to its original vision: the personal computer as a consumer appliance, a black box enforcing a very traditional relationship between the vendor and the purchaser.