How old are you? There is nothing wrong using proprietary formats and at the time there were no other alternatives. Macromedia were the pioneers of internet animation.
Even with HTML5 today there still isn't anything that allows me to produce a quick web animation with the likes of the Macromedia Flash. Adding that Flash would always produce the same result on any device that could support it. Mobile Phones, Symbian and even Palm tablets all supported it at one point.
Proprietary isn't the issue here, it's the monopoly that Adobe is. Adobe could of more and happy propped this up but no; like all major buyouts, bleed the product out to die. If it wasn't for Macromedia, Adobe wouldn't be what it is today.