You remove a bit of complexity. Sure Postgres is not hard to set up sn to connect to, but Sqlite is just opening a file. It being a file makes it also very easy to test or debug you application.
It is simpler and removes failure points. You don’t need a separate database server process or network/socket connections. Everything happens in-process.
postgres is great and is also a good default choice. It needs a bit more setup than sqlite. Unless I need a capability that postgres provides, I go with sqlite. It just works.