There's a lot of ongoing confusion about Flash's role in web animation so I've made this blog post as a reference point when it comes up in the future.
Flash was created in the late 1990s as a tool for animation and interactive media. Projects were exported as SWF files, which could be played in a desktop application or in a web browser, via the ubiquitous Flash plugin.
In 2010, Steve Jobs penned his Thoughts on Flash. Steve wanted to explain why iPhones would not be adding support for Flash but to avoid making it about computing power or competition with the app store, Steve went scorched earth. He had plenty of valid points, though; the Flash plugin was increasingly out of place as part of the open web.
One of the main points was that nothing the Flash plugin offers can't be replaced by HTML5, which is an open standard vs a closed system controlled by Adobe. This has lead to a lot of long-term confusion about Flash animation, however. For the past decade, I've continued to see people say how animators need to stop making animation in Flash and start making it with HTML5.
It is actually fine that animators continue to animate with Flash (now re-branded Adobe Animate). The only difference is now their animations must be shared in a video format (like MP4), rather than SWF.
So Flash animation never actually died, it just had to export to a format that doesn't require the Flash browser plugin.
On Newgrounds, we created Swivel and have made an ongoing effort to convert classic SWF animation to MP4 format. This is why you can view a lot of the animation on Newgrounds via your iPhone.
We more recently unveiled Newgrounds Player (Supporter only beta at the moment), a desktop player that integrates with the NG website to launch SWF files. You still earn medals and high scores in games, too!
Long-term we hope to emulate Flash in-browser but we wanted to have a solution ready in the near-term, since Flash plugin access is expected to become more hidden this July, before being removed from browsers completely in 2020.
In summary: It is 100% fine that animators are still animating in Flash. Don't tell them they need to animate in HTML5 because that doesn't make much sense. Much of the animation you enjoy on the web and even on TV is made with Flash / Adobe Animate.
FrozenFire
Adobe Animate isn't used professionally as much as you think. There are much better tools like ToonBoom out there now that are less prone to bugs, freezing, and shutting down without warning. I still use Animate for some elements, but ultimately everything gets imported into After Effects before a final publish anyways.
I think it would be better to say the essence of flash animation is not gone. There is no (updated) Flash software anymore, but there are several animation tools that allow online indie creativity to shine.