Nintendo filed a lawsuit against Pocketpair, Inc.

It has to do with how the statute is written (I used to do comparative international IP policy research and analysis). Japanese works are given fairly wide latitude in creative sectors based on artistic intent. For example, you'll see knockoff brands all the time in anime or manga, but the intent is clearly world building (or parody), not appropriation for promotional use. That artistic intent standard is used in the courts. This is why all the side-by-side comparisons people here probably saw on Twitter when Palworld came out was more of an ethnocentric American approach. Plus, copyright infringement is frequently incidental and not the result of large investment (unlike patents), so, in a country that prefers to handle domestic disputes informally, these incidents are less likely to go to court.

As a country that more recently entered the world stage based on manufacturing, patent protection is simply going to be taken more seriously as part of the culture. And yes--while I don't have numbers--patent litigation does seem to get thrown out often when it comes to video games, at least the high-profile stuff, anyway. Here's an example between Koei Tecmo and Capcom since I was already on Variety.