It was very accessible and I think it really made a difference that it appeared on a new computer that was supposed to represent the future of computering (i.e. had a GUI) yet was not meaningfully programmable out of the box, unlike the supposedly obsolete 8-bit computers it was replacing which came with BASIC. HyperCard looked like a thing that could fill that same ecological niche.

Edit: A bunch of takes from a few weeks ago https://news.ycombinator.com/item?id=40294301