Palworld had an insane launch peak of sales and concurrent users, but had relatively short legs (in recent days has been top 13-20 in sales) and bad user retention, most players ran away.
Since before its launch Helldivers 2 has been top 1 in Steam sales during a months and a half, and later moving between top 1 and top 2. Even if didn't reach a peak as high as Palworld in sales or CCU, Helldivers 2 had a great, way better than Palworld, user retention. So now and for a long period of time pretty likely Helldivers 2 will continue having a better CCU, specially if continues selling better than Palworld going forward, which I assume will be the case.
Helldivers 2 also has a bigger budget to keep improving the game with fixes, tweaks, new content and features which should continue improving the user retention and keeping it fresh to continue playing and and going back to the game.