HyperCard can’t be run on modern operating systems; it can only be run on older Macs or by emulating an older Mac. So it’s effectively dead. What challenges led to HyperCard dying?

HyperCard was commercial software, and at a certain point it was no longer advantageous to the company that owned it to continue developing it.

When Bill Atkinson started writing HyperCard, he arranged an agreement with Apple for them to potentially buy it. And Apple did in fact buy HyperCard. I haven’t found any thoughts Bill shared on what he would have done with HyperCard had Apple not bought it. But there was no open source software movement at the time that could have sustained development of it. And commercializing HyperCard would have killed an essential aspect of what made HyperCard what it became, the fact that it was free and “in the box:”

It was an exchange medium…You want people to be sharing stuff. They all have to have the software that it takes at least to play it, but hopefully to be able to author it also. So I worked out an arrangement with Apple that it would be bundled free, be in the box with every Mac…

(Legacy 10:37)

But the ability for people to share what they had created was limited from the start by Atkinson’s agreement with Apple, which prevented him from making it cross-platform:

…as I started with this idea, I thought, this has to be cross-platform, this can’t be Apple-only. And so I can’t work at Apple when I’m doing it. And so even as an Apple Fellow, I said “I want to go work on my own now. I’ll write some great software for the Mac, you guys will benefit, that’s not a problem.” They said “you gotta stick around here, they look up to you, admire you.” So I cut a deal, which is: “I’ll write this, and I won’t take any money from Apple while I’m writing it–I didn’t. And when I’m done with it, I’ll give you a right of first refusal, you can choose whether to accept it or not, and if you didn’t, that’s fine, but then it belongs to me.”…The devil’s part of the bargain was, if they did accept it, then they owned it lock, stock, and barrel, source and everything, and I didn’t have the right to commission a team to make a Windows version of it. So partly why HyperCard failed was that it was Mac-only.

(TWiT 29:35)

The next limitation that HyperCard underwent was Apple separating the player and the authoring environment:

And they were obligated to bundle it for at least two years. At the end of those two years, they got greedy and said “well we’re going to split it into the player and the authoring environment, and sell the authoring environment”…it killed it because all the schools and stuff, they didn’t have money to go and buy creative writing stuff from– I mean, it was free, so everybody would use it. And kids would make beautiful little stacks. And I saw the whole thing as an authoring environment…

(Legacy 11:07)

Ultimately, business pressures resulted in HyperCard being shut down entirely:

At a certain time in Apple’s life Apple was close to just plain folding and they had to do some really severe pruning to keep the plant from dying. And they just sort of cut everything that wasn’t essential, and said “we’re only gonna do a few things and we’re gonna do them well” and HyperCard didn’t make the cut. It wasn’t essential. And so it kind of got abandoned.

(Legacy 45:47)