I don't know, but there may be technicalities involved.

I've heard before that FIFA was able to have them, because the loading screen games were close enough to their actual gameplay (it was a simplified scene where you could pass a ball between 2-3 soccer players, if I remember correctly).

Well, and then there's also many games where the loading screen is 'hidden' in a section where your character takes an elevator or squeezes through a narrow path.

Ultimately, what even is a loading screen?
With a bit of a transition, you could argue that the minigame is actually part of the gameplay and it just happens to load things in the background.

So, it could also be the case that Namco never would have sued anyone, because a court clarifying the applicability could cause their patent to lose all value, as then everyone can do it in a non-applicable way.