Why does pg_stat_statement need to be included in shared_preload_libraries?

I am working on AWS RDS Postgres v9.6, and also v14. I noticed that in our shared_preload_libraries parameter, we have pg_stat_statement included. I don't understand why that needs to be there. In the Postgres docs , it says this: >The module must be loaded by adding pg_stat_statements to shared_preload_libraries in postgresql.conf, because it requires additional shared memory. This means that a server restart is needed to add or remove the module. However, several other extensions are already built in - for example we use dblink and hstore. These do not need to be in shared_preload_libraries. Why does pg_stat_statement behave differently? I think shedding light on this would help me (and hopefully others) better understand how built in libraries work, especially as regards the shared_preload_libraries parameter. The docs don't seem to say enough on this topic, or else I don't know where to find it.