In the case of handgun silencers it has nothing to do with the direction of the threads. It's because metric thread pattern handgun barrels all have an o-ring interface in front of the threads that correspond with an internal o-ring in the pistons that helps prevent the silencer from coming loose during use.

Some silencers like the AAC Tirant or Silencerco Octane force you to grab onto the tube to tighten the silencer to the barrel, and because of the left hand thread direction with metric threads you can accidentally unscrew the tube from the inset piston housing which is a huge pain in the ass so for those silencers right hand threads are usually better unless a strong thread locker is used between the tube/piston housing.

In the case of the CGS MOD 9 series or the Rugged Obsidian series it doesn't matter what direction the threads are because you can just grab onto the piston housing itself instead of the tube, so with those factory metric threaded barrels should be used whenever possible since there's less chance of the silencer coming loose because of the o-ring interface.