If you're talking about recursive common table expressions, those are called recursive, but are really iterative. The PostgreSQL documentation describes the iterative evaluation:

https://www.postgresql.org/docs/current/queries-with.html#id...

Note how there is no way to remove a row from the result set once it has been added. That would not be the case with a truly recursive query, because you would be constructing a new result set at every step. As a concrete example, try to write a graph query which finds all nodes exactly three edges from some starting node. That would be trivial with true recursion, but is impossible with a recursive CTE alone.