I blame Adobe for Flash dying much more than Apple. There's a lot of features that would have been hard to port (maybe Flash Player could have evolved into providing support for those and being optional for simpler content), but an HTML5 output that worked for 90% of 2D games and animations would have kept it relevant. Or at least funding Shumway while it was around if no one at Adobe was able to do it.

Instead they made a converter where you lost audio, video, scripting, effects, etc. It should have at least been able to convert a Homestar Runner cartoon.