And also, why do you care if some people _do_ want to continue developing Flash? It's going to get removed from browsers either way. The mere existence of a Flash player on somebody's desktop somewhere is not a security liability for you.
The argument presented was that open sourcing would allow that little bit of internet history to be preserved. My point is that you don't need source code for that. IMHO we don't want anyone to continue developing flash. Even it's creator has declared EOL for it. I understand there are people who want to mess around with it and do things that are potentially interesting, I object to disguising those desires as a preservation activity.
Just like with Java it's the Flash in browser that sucks, not Flash in and of itself.