Firefox now likes to block it by default...
So does Chrome. Also a lot of people on corporate networks with draconian security policies have had Flash blocked for years.
The biggest 'thing' about Flash today is all the major web media players ( YouTube, Blip, e.t.c. ) use it
But they don't default to it. If you want to view Flash in Youtube now you have to deliberately change to it in your settings. They started supporting a HTML5 option back around when iPhone launched and then just started defaulting to it about 6 years ago.
HTML5 + WebGL is not so great on phones and tablets.
But then neither was Flash. Even when Google was praising the Android because it supported it and the iPhone didn't, it was still very hit and miss.
On iOS when you couldn't run flash inside a browser, you could build it into a standalone app for the platform.
You could but at the time you reached the threshold bundle size that was permitted OTA (A do nothing Air to iOS program is 12MB). I think machinarium just managed to squeeze onto the iPhone.
Flash is still useful as a toolset and API. Adobe just need to drop the runtime and make it so all flash content just compiles to minified javascript.