In the 2000's, Flash was gaining a ton of popularity on the web, and Macromedia was recently bought by Adobe. They had just developed a new programming language, ActionScript, which was dynamic and object-oriented and offered an interactive developer playground. For early web developers like me, it was seductive and simple and more powerful than other state-of-the-art web technologies.
But, developers across the world, myself included, wondered: would ActionScript and Flash become open source? That was the one thing holding it back from broad adoption and improvement by the community. The web wouldn't stand for a closed standard.
I wasn't so sure what Adobe's plans were -- so I abandoned ship. Many others did, too. Of course, the rest is history: HTML5 technologies and JavaScript -- aided by canvas/svg/webgl and other standards -- have won the day.
My view is that openness always wins in the developer community in the long run.
Flash is now relegated to a "second-choice" technology for web applications, mainly used for some specialized rich internet apps, games, and backwards-compatible video players. I personally hope that Apple learns from this lesson and deviates from their history by making Swift free and open source software. It's not only better for the developer community -- it's also better for Apple.