Nope, it was the Flash runtime. That, and the fate of being a plugin that provides functionality that the browsers would eventually make part of the core rendering engines.
It created too many divergent paths for developers to follow. One of the great strengths of the flash runtime was how much easier it was to write something that would run in any browser, all with one clear API and one set of ui components that were easily extensible. Flex introduced far too many component sets and encouraged the creation of overwrought java-like frameworks. Eventually even js started looking better in comparison. The only reason they even did that was because they got greedy. They had a decent enough IDE with the flash authoring tool (although it needed additional support and features for pure actionscript developers), but they decided to throw their weight behind flex instead. Of course, flex was totally unusable for designers, and mxml was a godawful pile of shit, so they created catalyst to allow collaboration between designers and devs. Now you've got three different tools all targeting the same runtime, and they all suck. So now if you're just getting into programming for the flash runtime, you have to sort through all kinds of garbage to find what you're looking for, pretty much the same (if not worse) as scrounging around for js tutorials/documentation.
