Asset extraction is possible with any game, but I do understand the notion of not wanting to have your graphics and sounds just sit there for any "noob" to grab.
I did use Enigma Virtual Box in the past (Windows only I think), which is a free program for the purpose of creating portable applications for software that usually doesn't support this (would have to be installed).
It results in one single executable file and works flawlessly as far as I can tell. Your assets won't be visible to the user and they aren't temporarily being extracted to the hdd either.
Admittedly I didn't research this for safety and it might be a bad idea for other reasons. All I can say is that I didn't get any complaints related to this so far.
Once you realise that pirates aren't your key demographic it becomes less relevant to most developers.
In other words thats income you wouldn't receive anyway.
So true! I think the concern here lies more with the openly available assets in general though.