When HTML was limited, Flash was used by developers to add unique high-density animations, media, and other interactive elements like online gaming on websites but this year, online usage of Flash has dropped dramatically by 17% as sites have shifted to more innovative technology that don't require the Flash plugin.
When you go on Youtube, Dailymotion, or any other websites, they are using new and advanced codecs for streaming and video playbacks. It also became a favorite target for hackers and black hats for much of its existence leading most browser developers to block the plugin and it has always been a security issue. Adobe has also come under heavy criticism for not troubleshooting enough to fix this problem in fact they released apology at one point for taking over 16 months to fix one particular issue.
It was until 2015 that Youtube finally moved on and migrated away from Flash and opt for HTML5 but this multiple major flaws along with enormous improvements in open standards have continually eroded Flash's market share in the high-quality video and interactive web arenas.
In the late 2000s, open standards that provided some of the same visual and interactive functionality as Flash were really starting to take off and aside from using efficient hardware video decoding that Apple claimed could double screen time while watching videos, they were free.
Security patches for Flash will be available until 2020 for those still clinging to the plugin. Adobe's Flash player was revolutionary in its day transforming the internet from flat boring pages to interactive experiences. Flash hit 500 million downloads in the second half of 2013, with 300 million installations on Android and iOS alone.
Google acknowledges the contributions of Flash in history but added that:
“Flash was the answer to the boring static web, with rich animations, media, and actions. It was a prolific technology that inspired many new content creators on the web. It was everywhere.”
With all that said, when support for Flash ends in 2020, it won't disappear completely because there will always be old traditional websites that will never be updated. Offline Flash is still widely used in the animation industry even for current TV shows. It was once a prolific technology that inspired many new content creators on the web. Google added that most users and websites will not recognize any impact from this change.