So Flash and HTML/JS are how I got into programming at the age of 8, and I completely disagree with your comment.
All I needed to do was export the flash document as an exe and boom: it worked. The portability was amazing. I would just cut a release, put it on floppies, and take them to school. I never had anyone complain once about having an issue. Oh, and no one gave a damn about Linux outside of server admins back then, so yes an .exe was "universally" portable across whatever windows version people had running. There was also a fairly easy process for creating versions for Macs then too, but I don't remember how I did it.
Also, Flash was very good about having backwards compatible exports, so for as long as you weren't using the latest features you could reliably export to older versions of Flash.
Flash was a blessing in the late 90s and early aughts too precisely because it was the only reliable runtime when the internet was a flaming trash heap of incompatibility during the browser wars. Nothing worked everywhere /except/ Flash. The only other app platform available at the time were Java applets, and those were a nightmare. There's a reason why you used to be able to buy entire websites that were Flash based: it just worked.
Yes, Flash only worked if you had Flash installed, but honestly, who didn't? Was this really any different than making sure you had whatever God forsaken Windows service pack installed on your computer? And yes, I know Flash didn't work on Linux, but almost /everyone/ ran Windows back in the day.
I loved every product Macromedia created and owe a lot to them for having made it so easy to make engaging dynamic content. It's how I got hooked on developing software as a kid in elementary school.
It's a shame that there's nothing as simple anymore. I died a little inside when Adobe bought them, and I feel like the next generation is missing out on what was a really fun, flexible, and simple tool...
Making a ball change shades and move in Flash was a few intuitive clicks on a timeline. Now we have a only have a canvas API with relatively low level primitives. If you want things to be simpler, you have to go find some other package, oh wait now you need node, npm, we pack and 20 other dependencies to build the damn package, did you download the proper CSS file too, oh wait you need to import the script at the bottom of the page not the head, blah, blah, blah.
I miss Flash. Yes, the internet is better without it, but I feel like kids of today don't know what they're missing.