Animation studios. I know for a fact that Teen Titans was animated in Flash/Animate for its entire life, for instance; that’s directly from a former co-worker who was the animation director there. Lots of small productions, too. Animate is a lot cheaper than Toon Boom Harmony so tons of hobbyists use it.

The only difference between Animate and Flash is that SWF export got dropped eventually. And a haphazard smattering of new features got added.

You don’t play FLAs. You load them into the editor and output SWFs. Or various video formats. There are reverse engineered SWF players, most prominently Ruffle, but this is the first I’ve heard of anyone parsing FLA files.

FLA is the source format, it is to a SWF (or other video file exported from the editor) as a PSD is to a JPEG, or a .c file to an executable program compiled with all debug info off.