Since dot "." is already used to refer to columns, reusing it to refer to foreign keys would make parsing a lot more complex and error-prone, since the grammar

Since dot "." is already used to refer to columns, reusing it to refer to foreign keys would make parsing a lot more complex and error-prone, since the grammar would be context-sensitive, you would need to take into account you are parsing a foreign key join expression first, i.e. you wouldn't know what "foo->bar" meant without looking at the surrounding code. While probably possible, I think it would be less clear and also increase parser complexity more than necessary. My original idea was actually to use dot ".", but then others explained the above to me, which made me rethink.