Flash didn't die because it was bad.
The reason why Flash became so popular is that while the development tools cost money, the player was free for anyone to install. Browsers eventually started installing Flash by default (mostly so they could solve some of the security issues with prompt updates). By 2005, Adobe had a major monopoly on dynamic web content.
And then smartphones and tablets became a thing. Adobe didn't want to keep giving flash away for free, they wanted to exploit their monopoly for profit, by charging phone manufactures 25 cents per device for the right to include the flash runtime on their phones. Many Symbian, Windows CE, and later Android phones were paying this licensing fee to Adobe.
I suspect this royalty fee is large part of the reason why Job's "Thought's on Flash" letter came about. The letter mostly talks about need for open standards, and it is right. But I think Adobe's insistence on royalty fees really rubbed Apple the wrong way. Maybe if Adobe wasn't trying to extort smartphone vendors for royalty fees, it would have survived, and Adobe could still be charging money for the flash creative tool today.
Hell, if Adobe weren't trying to profit of the runtime, they wouldn't have had any objection to making the runtime an open standard and allowing anyone (including apple) create their own flash runtime implementations.
Flash didn't die because it was bad. Flash died because Adobe tried to exploit their monopoly for profit, and the wider industry responded to the threat.