Can't it? We never worried about cross-browser issues, because the plugin stabilized that for us. There also was a form that ran natively on mobile, called Adobe AIR. It's not like there are no security concerns with native HTML. A lot of the stuff we did quickly and easily with Flash you can't even do with HTML 5, and if you can it takes lots more time and effort.
I do believe that Adobe could have kept Flash, if it had gotten creative about how it marketed it. You can convince people to do things if you're good at marketing. But keep in mind, this was the second time Adobe had killed off a product I was making a living off. And what I didn't say in the story was that a couple of years prior to the official demise of Flash, I had offered to pick up the Atlanta Flash user group when it was left leaderless. Adobe told me that I could only do that if I'd lure users into their creative suite products instead of exploring Flash topics. This played into my decision not to share anything I was doing with my framework that truly leveraged Flash.
None of these companies give a crap about their users, so fanatical loyalty to any tool is not in developers' best interests.