So why doesn’t that tool exist?
Well... as far as I know it does. I’m pretty sure this is exactly what Adobe Animate is meant to be:
https://www.adobe.com/products/animate.html
So why isn’t it causing a Flash-style revolution?
In my opinion... Because of YouTube. Twitter. Etc.
Before everyone had heaps of bandwidth, you needed to consume smaller files. A full 1080p video was unfathomable with the codecs, compute and network bandwidth available in the early 2000s. Swf files however were small and easy to distribute. The perfect storm occurred due to the structure of early internet, and communities like Newgrounds flourished.
I honestly think Flash just got a bit stale. It stopped being new and exciting, and for animations video sites were probably going to win out anyways. For games, a lot of indie devs now target PCs and game consoles. Unity and Construct export to HTML5. People wanted to do more advanced things to the point where Flash itself started doing things like 3D rendering, at which point the appealing aspects of Flash started to make less sense anyways.
Many seem to argue passionately, probably from an emotional place, that Flash was killed. Honestly, I just don’t agree. Flash was dying either way. Everyone just gradually decided to cut off the life support.
The era it ushered in will be missed, though.