Honestly why hasn't there been a flash-like competitor or alternative that has filled the gap of creatives being able to quickly produce content and distribute it easily on the internet? I think the HTML5 folks envisioned <audio/> and <canvas/> being all you need for interactive stuff, but that hasn't really come to fruition. For animated content, is it perhaps YouTube that took over?
I'm always amused by this question.
There is, it's called Adobe Animate, its what they rebranded Flash as, it's literally the same thing. It exports straight to Canvas and WebGL using the create.js libraries. [0]
Basically the online advertising space had a collective heart attack when Flash was suddenly deprecated because they used Flash for all their banner animations. Adobe tried to replace Flash with Edge [1], which was one of the slowest and buggiest program I ever used. It didn't last long.
[0] https://createjs.com/ [1] https://en.wikipedia.org/wiki/Adobe_Edge
I think kids just jumped onto Unreal, Unity and Blender instead of bothering with 2d.