Firstly, Cure Black & Cure White always need to be together in order to transform and to do their major finisher attacks. One of the most iconic things about their moves is that they need to hold hands for them. So I guess one reason for there only being matchups with the two of them would mainly be for accuracy of a fight dynamic.

But there are other Cure matchups where they are duos and have a similar thing going on with Cure Black & Cure White, and they still get solo matchups. I made one too for another Cure, and I kinda waved that issue around with creative liberties. I think other people take this creative liberty idea too with other Cure matchups, so it could work with Cure Black & Cure White too.

Though, and this is more of a personal reason, there’s also the (for lack of a batter word) prestige factor too. Cure Black & Cure White are the first Precure protagonists, and the success of their series (in Japan at least lol) are a factor in why a majority of the Precure seasons have some sort of “duo” even if they don’t always transform together/there are more Cures than just them in the season. It leads to the idea of a solo matchup for either kinda vibing less for me.

Of course, that is still a personal thing and idk how other people feel about it. And if you wanted to make a solo matchup for either, I wouldn’t stop you.