Houkime, I am also a FOSS (Free and Open Source Software) advocate here; really heavy into Linux-based kernel debugging, contributor for 'Battle for Wesnoth', and relentless retro gaming enthusiast.
I understand your fervor and passion for FOSS but you have no fucking right to complain to the dev that they made 'bad choices' because they didn't FOSS their game. How dare you!?
FOSS is something the DEVELOPER must choose of their own free will. Neither you nor anyone else have the right to complain about it. A majority of games are closed-source and that's how they wanna do it. You live with it or go play any other FOSS game you like. You enjoy Endless Sky? I played it for a bit and it was ok for me. Needs a bit more work to really compete with some other 2D shooters.
Personally I used to be a fan of this 'Asteroids-style' game that I won't promote here (it is on Steam) but the devs of that game promoted pay to win and forced-PvP in that game due to a lack of content (abandoned for years now).
I do my best to be supportive of EVERY indie dev that makes a good faith effort in actually delivering a solid relatively bug-free experience that is enjoyable without resorting to exploitative gambleboxes like every other game has done.
If you want to ASK them to FOSS? Ok. But you don't ever have the right to DEMAND that they do so. Remain polite and stop giving the FOSS community a bad name :P