That's because using the foreign server is difficult for the user.
For example, the user doesn't always have the permission to login to the forein server.
In some cases, the foreign table has been created by the administrator that has permission to access the two servers and the user only uses the local server.
Then the user has to ask the administrator to run TRUNCATE every time.
Furthermore,there are some fdw extensions which don't support SQL. mongo_fdw, redis_fdw, etc...
These extensions have been used to provide SQL interfaces to the users.
It's hard for the user to run TRUNCATE after learning each database.
Anyway, it's more useful if the user can run queries in one place, right?
Do you have any concerns?