Flash was basically a remote shell with some animation tools on top. The Windows malware hell of the early 2000s, with random websites (even a banner ad on the New York Times once) doing drive-by-installs of early ransomware. (Thankfully, cryptolocker ones hadn't started yet...) And if you were a Windows escapee, the Flash experience was absolute trash on OS X and Linux.

It also became clear that the source code was borderline unmaintainable and/or Adobe lost everyone who knew or cared about it after they bought Macromedia.