Flash (and Flex as collater damage) got killed by Apple.
But yeah, I agree even now, nothing compares to Adobe Flex on the developer productivity aspect
Flex was better than anything in use for web front end to this day, imo. Aside from requiring Flash, but iirc targeting HTML/js as an output format was on the roadmap.
We have Apache Royale https://royale.apache.org/ for that. Compile your Flex MXML + ActionScript to HTML + JS and more.
Yet, as a user, there's nothing I dreaded more than the all-Flash application. Binary blob, no integration with the OS, and accessibility was an afterthought. Basic things like highlighting text to copy, tabbing between controls, Enter to submit, would not work. We should take care to not view the history of Flash through rose-tinted glasses.
I know some people think that. Personally, I hated both the programming model and the interfaces that resulted from it. It was much worse than the competitive HTML/CSS interfaces of the era to actually use in most cases.
Flash got replaced by Animate CC and they still sell Dreamweaver, but it not quite the same.