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.
Anbernic devices in particular are known to ship with an SD card that’s preloaded with a fairly large game library. I own a RG351M which did indeed include a cheap card loaded with both the OS and a collection of games by Nintendo, Sega, and many others, plus some strange rom hacks. I immediately swapped that card out for a better one with a better CFW and my own files.
Most other notable names in the emulation handhelds space like Retroid, Ayn, and Ayaneo expect users to be able to provide their own files instead, which I’d say makes more sense.