I don't get it. I mean I get it because it's Ninty, but I don't get why now?
Has there been something in a major new feature update that has finally tipped the scales into clearly taking the piss, or have the legal team at Big N finally seen their erections subside after the game's launch and only now can move enough to do something about it?
Considering they're going for patent infringement and not copyright infringement, it's possible it just took this long for Nintendo's legal department to find something even remotely tangible that they could sue over. And since they haven't said what patents Palworld infringes on, I have to assume whatever it is, is very flimsy.
Despite their reputation for being quick, my opinion is that Nintendo does often take their time. Most of the things they take down do exist for months or years (and also follow the same format of a ROM hack that got a lot of attention so easy copy paste). My assumption is they're just dotting their i's and crossing their t's and patent is just what they think they'll have the best chance at winning.
Going back to Yuzu, Nintendo was in Discord and all over the place monitoring and collecting evidence even since Tears of the Kingdom launch. It took almost a year before the final attack with overwhelming number and secured evidence. Nintendo is not fucking around and is serious, that's for sure. So if Nintendo attacks, they often have a point or (legal) reason to.
That's why I'm so curious in this case. I would hope that Nintendo being (legally) wrong for once.
My best guess: whatever they're filing now was so exhaustively researched that it took months to prepare the strongest case they're able to make, possibly delayed by the lawyers working on several other cases. Plus waiting until sales have dried up can maximize damages.
Another possibility is that Nintendo/TPC is planning to make some big Pokémon announcements soon and wants to target this shortly before their own new games to reduce competition. Palworld might seem like more of a threat to the execs now that Pokémon is nearing a major release than it was in the middle of a long drought for the series.