Adobe's lack of interest in making the Flash runtime a quality bit of software killed Flash. At the executive level Adobe was only interested in selling authoring/server software and only supported the Flash runtime as much as necessary to sell that software.

Microsoft and Apple hated it because the plug-in was a top vector for malware on their OSes. Browser vendors, so Microsoft and Apple plus Google and Mozilla, hated it because it was a top vector for malware in their browsers and forced their hand with respect to plug-in APIs. Apple triply hated Flash because it's performance on the Mac was terrible compared to Windows. That was the status quo before the iPhone was released.

Flash Lite on early smartphones was barely Flash. It was more an ActionScript 3 runtime with a limited version of Flash's drawing engine. It couldn't play arbitrary SWFs on the web.

The Flash plug-in Adobe eventually released for Android was also pretty awful. It had terrible performance and was a battery killer. SWFs designed for WIMP desktops also worked for shit on touchscreen Androids. The plug-in was terrible at translating touch events to click and drag events. It demonstrated pretty clearly every argument Apple made about keeping it off the iPhone.

Adobe was not a capable steward of the Flash plug-in/runtime. What little effort they devoted to the plug-in was focused almost entirely on the Wintel platform with all others being effectively ignored.

Adobe killed Flash by a thousand tiny cuts from mismanagement and lack of interest. Their business model for the past two decades has been rent seeking on products they bought with Photoshop money and then stuck in maintenance mode. They were only interested in Flash insofar as it would allow for more rent seeking.

It was never going to be mobile battery friendly, so it was not going to survive anyway