Just to clarify - we're not even talking about the adobe's flash plugin. There is no source code for it, so we can't physically port it. We're talking about separate flash language interpreters, based on whatever few pieces of information about the language specification Adobe has released, guessing games and reverse engineering. So even if we somehow ported Gnash or whatever else there is, most of your games would have glitches, if they ran at all.
Who's to blame? Adobe - popularizing a closed format with a narrow range of compatible platforms.