As you pointed out in your next paragraph, it was because that way Adobe can point a finger at Apple and say "it's them to blame". This blog post [ http://www.kaourantin.net/2010/02/core-animation.html ], quite similarly informative as the one astrange linked to, describes very well part of the reason why the Flash plugin is a dog on Mac OS X. I can only add to it a detail that is not explicitly mentioned in there - the drawing contexts mess and lack of support (e.g. OpenGL) is only applicable to NPAPI plugins. WebKit has an alternative, modern, clean, and fairly flexible plugin API. So if Adobe really wanted to make Flash highly performant on Mac OS X, they could have done what Apple do with their Quicktime plugin - have an NPAPI one for compatibility and have a WebKit one for performance for most users.