Back in the good ol’ days, Flash was very popular among many for playing media. It was used, online and offline, for displaying animations, showing presentations, and general advertising. Though there weren’t all that many options back then, such popularity still came mostly because it was simple. It was able to animate vector art very smoothly as opposed to large, clunky .gifs, as well as allow users to use simple interactions like mouse clicks and keyboard input. Macromedia Flash itself also had a very simple interface and UI, and was used in schools all over to help teach students multimedia and animation.
As the internet evolved, so did Flash. As video playback started to become popular, Flash had no choice but to adapt to keep up with competition and provide its users with the best experience possible. This involved cutting corners, taking back-doors, and even adding a whole new programming language to the mix at one point.