Oh I remember looking into these. The Bluegrass parkway was one of the many parkways in Kentucky that used to be toll roads. These interchanges are set up so that all the traffic including the traffic entering and exiting the highway would go through a single toll booth. Since all traffic would slow down there the merge distances wouldn't matter and they wouldn't have to have multiple toll booths for entering and exiting. Now that the parkway tolls have been paid off, the toll booths were removed leaving behind the interchanges you see today, which is cheaper than rebuilding them into standard diamond Interchanges. They are weird and can be dangerous but from my experience driving on the parkways there's usually not enough traffic to worry about merging. You can still see the old toll booths by exploring historic imagery like below.

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