I think the loss of these tools has less to do with the death of flash, and more to do with the decline of the genre of "internet ugly" cartoons and free games as a whole. We have technology in the browser that is just as powerful and just as portable (case in point canvas), but we rarely see it being used in the same way to build the same variety of browser games and experiments.
I know a lot of people talk about the tooling not being there, but I'm not sure that's the case. Web development is a very open field, there is a ton of documentation, and a lot of easy ways to get started. Just open developer tools in your browser and you can write Javascript - things were never the easy with flash. There's also plenty of free tools for building things with, from game libraries to animation editors, to IDEs.
I think the bigger issue is that the audience isn't there in the same way. Partly that's culturally - part of the glory of that era of internet was proper reveling in crappy animation, gross-out humour, and absurdism. But that's no longer part of the cultural zeitgeist in the same way. As a result, the cultural force behind a lot of the early examples of the medium has died out.
But also, and I think more importantly, the platforms have evolved. Animation still exists, but it looks different and tends to be hosted on YouTube or TikTok, because that's where people are. Games still exist, but now they're usually mobile games, because it turns out people like playing these games on the loo, and mobile browsers suck. And both of these platforms have their own advantages for creators: they both make monetisation easier, and they make it harder for other people to steal your work - both things that flash creators spent a lot of time worrying about.
Even as flash was dying, if it was culturally necessary to maintain, people would have done so. We had the tools and we had the technology. In fact, people did - I remember people pushing "HTML5 games" for a while, but they were never any good because no one had been making good news games for a couple of years at that point. In the end, flash died for much the same reason that non-threaded forums and IRC died - the cultural forces that used them either died themselves, or switched to other systems.