Because with git you have to explicitly push. Both have their valid uses; I use the git solution for a devops password database shared with a small number of colleagues. I use SyncThing to share a common subdirectory of a private password database with my partner.

SyncThing has the benefit of transparently handling the synchronisation behind the scenes for me. Whenever I place something in pass in the 'shared' subdirectory, it will end up in her database as well as soon as both our devices are online.