Well, I can't speak for others, but my personal experience with math tends to be that I only start properly learning why something works once I have the rules pretty well memorized. Before that, my working memory is so occupied with trying to just remember how to apply the rules that I don't have the space to remember why they work. Or alternatively, I can learn why the rules work - but in that case I don't have the memory capacity left for remembering how to apply them.

Of course, this is complicated by the fact that during the process of trying to memorize the rules, I often stop to think about why they work in an attempt to rederive them and make sure I'm not misremembering them. So it's not pure rote memorization, like the way it seems to be with DragonBox. But I would still expect that if somebody first learned them as meaningless rules in the game, and was then later taught math and the reasons for the rules, they'd have a good chance of being delighted at discovering where the rules came from, and could spend all of their cognitive capacity on developing an actual understanding.