I also don't know.The developers choose if it requires a membership for online? Doesnt that remove the whole point in the membership, and why would any dev make it require a membership, as more players will play your game if it costs less and has more features
From the start, I told myself that and thinked it was a bad move by Nintendo. I still think that today, but apparently it still work ? idk, it a weird decision. But anyways, Nintendo are the genies here, they probably have something behind their head... probably.... i hope....